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Full text of "Photographed spectra; 136 photographs of metallic, gaseous, and other spectra printed by the permanent autotype process, with introd., description of plates and index, and with an extra plate of the solar spectrum (showing bright lines) compared with the air spectrum"

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During the course of the last and the preceding 
winters, I was led, in connection with an investigation 
bearing on the Spectrum of the Aurora, to take photo- 
graphs of certain of the metallic and gaseous Spectra 
with a spectroscope of moderate dispersion. After a 
time this work gradually extended itself, and ultimately 
a very considerable collection of such photographic 
plates was obtained. In these labours I was very 
efficiently assisted by Mr. G. H. Murray of the Surrey 
Photographic Company (who superintended the photo- 
graphic department), and by Mr. E. Dowlen of Guild- 
ford, to whom I am much indebted for notes and general 
assistance. The photographic impressions comprised 
all that could be obtained of the spectrum in each case, 
ranging from about b to beyond H^ H^ in the violet. 
It was soon apparent from an examination of the plates 
obtained, — 

1. That considerably more of the spectrum was 
obtained in the direction of the violet end than 
is ordinarily delineated in the published works 
on Spectra. 



2. That, notwithstanding the moderate dispersion 
and the limited extent of the spectrum obtained 
(for want of the red end), each individual 
photograph had, without actual measurement 
of its principal lines, a separate and distinct 
character, easily recognised when once seen, 
and distinguishing it from all others. This 
peculiarity we think will be borne out by an 
examination of the Plates produced, and we 
ourselves had several practical instances of its 
application in our process of taking the photo- 
Under these circumstances we considered we might, 
with probable advantage to others engaged in spectro- 
scopic research, reproduce a series of our results as 
forming at once a handy book of reference to spectra 
in general, and as also illustrating in each particular 
case the peculiar features of the spectrum photo- 

The spectroscope employed (for the metals) was 
constructed by Mr. John Browning some years ago 
specially for Auroral observations, and is of the direct 
vision form. 

The prism is an inch aperture compound (5) one, 
dividing very easily the D lines with a low eyepiece, 
a similar second prism can be slipped in for use if 
desired. The collimator carries an 1^ achromatic lens of 
6 inches focus. The ordinary observing telescope and 
eyepiece were removed, and an 1^ achromatic projecting 
lens of 9 inches focus was substituted for them. The 


short tube carrying the last-mentioned lens was con- 
nected by a black velvet bag, with an ordinary square 
camera for plates 4 J -f 3 J, and the images were taken 
upon collodion wet plates. (See Frontispiece for 
arrangement of apparatus). 

The metallic spectra were obtained of tjvo sorts : 

1. By the spark. 

2. By the electric arc. 

The metals employed mostly formed part of a 
German cabinet which came into our hands with a 
good character. 

For obtaining the spark spectra, the apparatus con- 
sisted of a large EhumkorfFcoil, giving, with four double 
plate half-gallon bichromates, a thick strong spark 
about 2 inches long. In the circuit was introduced a 
condenser, composed of 4 glass plates, each containing 
50 square inches of coating. By this condenser the 
spark was reduced to one from ^ to ^ an inch long, 
and of considerable brilliancy. The time of exposure 
in the case of the spark spectra varied very con- 
siderably, averaging perhaps 15 minutes. 

For the arc spectra 40 pint Grove cells (except in 
one or two instances when 30* only were used) were 
employed, and with these the arc was steady and of 
sufficient length. In all cases the slit was placed 
vertically ; and in our printed Plates we have followed 
the usual practice of spectroscopists, in keeping the red 
end of the spectrum to the left hand. Care was taken 
to have the carbon points and cups well cleansed, and 
by trial plates, taken from time to time, it was seen 

B 2 


that they contained no impurities affecting the spec* 

For the spark, wires or points of metal, held by 
miniature steel pincers, were used. 

In the case of the arc, sometimes fragments of the 
metals, sonaetimes the metal in powder, and in a few 
instances solid metal electrodes were employed. The 
time of exposure in the case of the arc ranged from 
three to five minutes, according to the intensity of the 
stream of hght. The length and brilliancy of the arc 
were found to alter much according to the nature of 
the metal placed in the cup. The spark also varied 
considerably in length and intensity according to the 
electrodes. In the spark spectra, the air spectrum is, 
with a few exceptions, seen in company with the metal 
lines, the latter being, however, easily distinguished 
from the former by their passing only partly across the 
spectrum, while the air lines cross it entirely. 

In the arc spectra some carbon lines of constant place 
seem the only foreign introductions into the system of 
metallic lines. These carbon or, as we called them, 
' point ' lines, are found useful in placing and compar- 
ing the several spectra when obtained. The images as 
thrown on the camera plate were rather more than 
two inches long ; and these were subsequently enlarged 
exactly once. The lines required very careftil focussing, 
the slit being in most cases fine, so that where lines 
are found thickened it is in general due to their 
character. To supply the want of an approximate 
scale, and also to indicate the part of the spectrum. 


photographed, I prepared a diagram in which two 
spectra of the metal manganese were respectively com- 
pared, and a scale obtained by direct interpolation. 
The upper horizontal spectrum was a photograph ob- 
tained from manganese in a rather weak arc (30 cells). 
The vertical spectrum was an enlarged (by photo- 
graphy) copy of Monsieur Lecoq de Boisbaudran's 
normal spectrum of chloride of manganese (' Spectres 
Lumineux, Atlas,' Plate xvii). The curve obtained was 
regular, and a subsequent comparison of the result with 
the solar spectrum of the same instrument (Plate xxi) 
is satisfactory. The scale in most cases fairly coincides 
for the principal lines with Monsieur de Boisbaudran's 
spectra, but instances will be found where the photo- 
graphed spectral images are not in themselves ab- 
solutely uniform in exact length and position of 
fiduciary lines. The causes of this are not yet fully 
worked out, but we believe the result to be due to a 
difference in certain cases in distance of the discharge 
from the slit. To the Description of the Plates are 
added some notes by way of information as to the 
behaviour of the metals and on other points. 

The wave lengths of lines (where given) are 
taken partly from M. Lecoq de Boisbaudran's work, 
'Spectres Lumineux,' and partly from Dr. Watts' 
' Index of Spectra.' The photographs were all taken 
on separate plates, and have been very well re- 
produced and printed in permanent pigments by the 
Autotype Company, in compared sets of four. They 
are for convenience arranged in alphabetic order, 


the upper metals in the plates being selected for 
arrangement where electrodes of different metals were 
employed. Spark and arc spectra of the same metal 
are in many cases compared. A few of the metals 
and metalloids are wanting, mainly from the diflSculty 
of obtaining with our apparatus, spectra bright and 
permancDt enough to impress images on the photo- 
graphic plates. The arc photographs might with 
advantage bear considerably greater enlargement, but it 
was thought convenient to keep them, for the purpose 
of comparison, of the same size as the spark spectra. 
Some of the metals do not show their full set of lines, 
probably for want of more coil power; but there 
were considerations why a moderate spark was 
originally selected, and the spectra were subsequently 
kept uniform in this respect. 

When rough lumps of metal were used for points 
the spark was generally winged (especially when the 
batteries were fresh), and played about over the surface 
of the metal. The wings of the spark were tinged 
with green in the case of silver and copper, with red in 
that of iron, white or bluish white with magnesium. 
Titanium ore gave occasional flashes of red (probably 
from the iron clips), sodium gave a bright yellow flame, 
l^he cups used with the spark apparatus were of 
aluminium, except where glass is mentioned. 

Width of slit averaged -003 inch, except in one or 
two instances which are especially mentioned. 

When diflferent metals were used as terminals, the 
current was generally reversed in the middle of the 


The carbon terminals used in the arc were cut 
from ordinary gas carbons, 3 centimetres long and 6 
millimetres square. Those for the negative pole had 
one end filed to a point. Those for the positive pole 
were hollowed out at the end with a drill so as to form 
a cup. To get rid of impurities (of which iron formed 
the principal part), the carbons were soaked alternately 
in acids and water : First, they were soaked in 
diluted sulphuric acid, 2 parts water, 1 acid, then 
soaked in water. Secondly, in dilute nitric acid, equal 
volumes of acid and water. Thirdly, in hydrochloric 
acid, half volume of water. The acids and water were 
changed several times during the soaking. Last of all, 
the carbons were soaked in water alone, which was 
repeatedly changed imtil all the acid was washed out. 
They were then slowly dried in an evaporating dish over 
the flame of a Bunsen burner. The acids were all pure, 
and the water distilled. The whole process occupied 
from one to two weeks, according to the density of 
the carbons, some being more porous than others. 

When metals in powder were used in the arc, 
small beads of the metal were usually scattered over 
the inner surface of the cup, the main portion of the 
metal remaining at the bottom. 

All the metals of the iron group gave out sparks, 
viz., manganese, iron, cobalt, nickel, chromium, and 
uranium. Silver gave a melted bead, which revolved 
in the carbon cup without actual contact with it. The 
width of the slit was generally '001 inch, distance of arc 
from slit 1^ inch, but from the flame playing round 


the point and cup, this distance was subject to varia- 
tion. The adjustment for distance of arc discharge 
was by rack work worked by hand. The upper 
carbon was fixed in a ball-and-socket joint so as to 
adjust easily over any part of the cup. 

A fresh pair of carbons was used for each metal. 
Much trouble was found in keeping the slit, and the slit 
plate clear from metallic beads and other impurities. 
It would be a great advantage for fiiture similar work 
to have the whole slit plate gilded and the slit jaws 
formed of obsidian, platinum, or gold. 

The gas spectra are represented in the last fifteen 
Plates ; and for the purpose of obtaining these it was 
found necessary to resort to a difierent form of instru- 
ment to that employed for the spark and arc spectra. 

An attempt was at first made to take all the spectra 
with the same instrument, but it was soon found that less 
dispersion and a brighter image would be required to 
give any useful results with the gases, and one only of the 
series (viz., spark in coal gas), was taken with the same 
instrument as the metals. 

Three forms of instrument were then arranged and 
used for gaseous spectra : — 

A — A compound (5) direct vision prism on stand 
similar to that used for the spark and arc spectra, but the 
colhmating and projecting lenses of the spectroscope 
were replaced by two camera lenses of somewhat larger 
diameter, and each of 4| inches focus. The image was 
fairly bright, but not very sharp, as the slit could not be 
made very fine without loss of light. 


B — A table spectroscope constructed for me by Mr. 
Browning with two quartz (inch) prisms of 60° angle, 
the coUimating and projecting lenses being also of 
quartz 1^ inch in diameter, and of 6 inches focus. 
The images with this instrument were brighter than 
those with the last instrument (A), were of fair defini- 
tion, and penetrated more into the violet. 

C — This last instrument was also a table spectro- 
scope, made for me by Mr. Browning, with a view to 
the photographing faint spectra. 

The prism is a large compound (3) one, IJ inch 
high, 2 inches across' and 4f inches in its longest base. 
The colhmating and projecting lenses are from a fine 
field glass 2 inches in diameter and of 7 inches focus. 
Our experience led us to conclude that considerable 
aperture of prism and of lens was absolutely essential 
for the production of bright and sharp images. This 
Mr. Eutherford had previously demonstrated in 
America. The images from our instruments of small 
aperture bore no comparison whatever with those 
afforded by the larger instrument now describing. 
With the latter the images were very bright, and the 
lines wonderfully well defined and separated for so 
small an amount of dispersion. The impressions are 
quite small on the photographic plate (less than half an 
inch in length), but so sharp that they would bear 
enlarging nine or ten times • without material loss of 

In the Plates of the gases the images obtained from 
spectroscope A are enlarged twice, those from spectro- 


scope B, (quartz), are also enlarged twice. Those from 
spectroscope C are enlarged rather more than five times. 

The spectra from A and C spectroscopes are en- 
larged so as nearly to correspond in dispersion and in 
actual dimension. Those from the spectroscope B 
(quartz) are on a smaller scale altogether, and are 
mainly used where comparison of spectra is desired. 

The spectra of the gases (except in one or two cases) 
were obtained from the exhausted tubes of the Geissler 
form commonly used in spectroscopy, some of foreign, 
some of home preparation. The latter were found best 
adapted for our work, being larger in the bore and bulbs, 
and bearing stronger currents without injury. For 
working the tubes, two different coils were used. The 
smaller one was a half-inch coil such as is generally 
sold for the purpose of hghting up tubes in spectral 
work, and was excited by a quart bichromate. The 
larger coil was that employed for the spark spectra 
before described ; it was worked by two half-gallon 
bichromates only. This instrument has a large heavy 
break of the common form, but with screw adjustments 
enabling the rate of vibration to be easily controlled 
during work ; a very steady current was obtained by 
this means. The smaller coil was used for single tubes ; 
and such as would hght up easily. The larger coil 
was used in cases where two tubes were employed, for 
line spectra and for tubes which required much lighting 
up. When line spectra were wanted, the condenser 
before mentioned with two plates taken out, or a 
small Leyden jar was introduced into the circuit, the 


rate of discharge being regulated by the distance be- 
tween two platinum points on a stand, which formed part 
of the connections. When the large coil was employed 
for a single tube, a second larger tube was usually 
introduced into the circuit to diminish the heating 
effect of the current. The time of exposure for the 
tubes was about twenty minutes with spectroscopes A 
and B, and from tw^elve to fifteen minutes with spectro- 
scope C. The tubes which lighted up most easily and 
were not damaged by the continuous current, were 
nitrogen, carbonic acid, coal gas, cyanogen, hydrogen, 
oxygen, silicic fluoride, and olefiant gas. All these 
photographed more or less easily. The tubes which 
gave us more trouble were bromine, iodine, chlorine, 
ether vapour, turpentine vapour, sulphur, and tin 
chloride : bromine and chlorine we failed to get 
photographs of. These tubes broke down before they 
had been lighted a sufficient length of time to 
impress an image. Iodine vapour tube failed also in 
this respect ; but we succeeded in photographing 
(though not well) the spectrum of the spark in a bulb 
filled with iodine vapourised. The tin chloride tube 
also soon broke down, and we obtained only one plate 
from it. Further particulars of the behaviour of the 
tubes will be found in the Description of the Plates. In 
all cases a photograph was first tried of the single tube 
as filling the whole length of the slit, this last being 
intentionally as long as the instrument would bear. 
When the slit was reduced in length, whether by the 
comparison prism being used or in any other manner, a 


manifest falling off of the photographic effect in point of 
brightness of image was apparent. It was only with 
the instrument C that we could use quite a fine sht. 
In the course of our experiments we tried the effect of 
an electro-magnet upon some of the tubes. Our 
magnet was one of Ladd's, of the size used for dia- 
magnetic experiments, with arms 10^ inches long and 
poles 2 inches across and with large movable coils of 
insulated copper wire. It was excited by the four 
half-gaUon bichromates before referred to. Probably 
with more battery power we should have obtained 
changes in the spectra themselves in accordance with 
the experiments of Monsieur J. Chautard. It was, also, 
unfortunate that chlorine, bromine, iodine, sulphur, 
and tin chloride, from which he obtained his best 
results, were just the tubes which gave us the most 
trouble in a photographic way. The magnet was fitted 
with conically pointed armatures ; between the points 
of which we placed the capillary part of our tubes. 
In this way danger arose to the tubes, as the armatures 
when the current was passing would draw together 
with sufficient force to crush the glass. We secured 
the armatures in their places by turning out circular 
edges on their bases, and so arranged that the blunted 
points would just take the thickness of the tube between 
them. Our experiments were mainly without much in 
the way of positive 'results. The stream of light was 
in most cases narrowed, and appeared to experience a 
certain amount of resistance in its passage (in the case 
of siUcic fluoride a sort of sharp whistling sound was 


heard when the magnet was excited), but we did not 
detect any palpable change in or addition to the 
spectral lines. Only in the case of nitrogen did we get 
any very marked effects, and this was somewhat 
peculiar as M. Chautard classes this gas amongst those 
upon which ' the influence of the magnet is hardly per- 
ceptible,' (' Phil. Mag.' S. 4, vol. 50, p. 79). A Geissler 
nitrogen tube having been placed between the poles of 
the magnet, it was lighted up by the small coil. The 
stream of light was steady and brilliant, and (except at 
the violet pole) of the rosy colour peculiar to a nitrogen 
vacuum tube. On the excitation of the electro-magnet 
the discharge at once appeared diminished in volume, 
with an apparent increase in impetuosity ; and not only 
the capillary part but in a less degree the bulbs also of 
the tube changed from a rosy to a well-marked violet 
tint. We several times connected and disconnected the 
magnet with its batteries, but always with the same 

This effect of shifting tint was very striking, and 
assuming the Aurora to be wholly or in part of electric 
origin, is strongly suggestive of a reason for the varying 
tints of the streamers which are frequently observed. 
Of the spectrum of the capillary part of this tube we 
took two plates, taking care that all things should be 
as equal as possible, the apparatus undisturbed, and the 
time of exposure exactly the same. One plate was 
taken while the tube was in its normal condition, the 
other while the tube was influenced by the magnet. 
The plate H- magnet will be seen to penetrate more into 


the violet, though the character of the spectrum itself 
does not appear altered. An eye- view of the tube 
with the spectroscope also showed us no definite 
variation in the spectrum, nor could we trace 
that the violet pole spectrum extended itself under 
the altered condition of the tube as to tint. We 
tried also a large bulb Plucker tube in which the aura 
from the violet pole was condensed into a bright arc 
under the influence of the magnet. No change of the 
violet tint was here remai-ked, but only a brightening of 
the light consequent upon its condensation. Plates in 
this case also gave slightly more of result in the violet. 
In the case of silicic fluoride the stream of light was 
diminished in volume, and the plate from the tube 
without the magnet is decidedly the brightest. In 
other respects the plates are alike. 

Our experiments of course do not conflict as com- 
pared with M. Chautard's, as the battery employed on 
our magnet was far inferior in power to his (he used 
from twelve to fifteen large Bunsen elements), but our 
experience with regard to the nitrogen lube seemed 
worth recording. 

Li taking our spectra, and specially the gases with 
spectroscope C, we had to exercise great care in the 
focussing on the plate. For this purpose the finest 
ground glass for the plate and a strong magnifier to 
view the image were employed. The rough adjust- 
ment was first of all obtained by moving the camera 
on its heavy base, and the fine adjustment was then 
completed by means of a screw motion in the same 


base. It must not be supposed that the Plates printed 
were all we obtained, probably not more than one in 
three which were taken were selected for enlargement. 

In nearly all cases we took two plates of the same 
spectrum, although the first might be good ; and fre- 
quently from the heat of the room and other causes 
plates good as to spectral image were imperfect as 
photographs. In fact anyone wishing to try the same 
work on the same or a larger scale must expect partial 
failure and disappointment, until experience has been 
gained in it. Kennett's dry plates would have some 
advantages over the wet plates we employed, but they 
would also be subject to the drawback of taking longer 
to develop, so that except with the loss of much time, 
one could not, as we did, develop and examine the 
plates obtained at once and before the points and other 
apparatus were displaced for a next experiment. Our 
results of course are not intended to be placed by the 
side of photographs of spectra of larger dispersion taken 
for comparison of the metals, study of the solar spectrum, 
etc., but they may perhaps prove useful to amateurs 
and others, working with spectroscopes of small dis- 
persion, for comparison of spectra in their general aspect, 
and for study of the points and peculiarities attaching 
to most spectra, which are generally brought out 
in our prints. To those v/ho have the time and 
opportunity there seems much to invite a taking up of 
the whole subject on a more extended scale and with 
more complete apparatus. 

Absolute truth is everything in spectroscopic work, 


and the very best drafitsman working with the most 
perfect micrometer cannot, even at the expense of a 
vast amount of labour, equal in accuracy a good photo- 
graph of a set of spectral lines. Photographs, too, have 
the great advantage that they may be enlarged and 
tested at leisure ; and if several plates of the same 
spectrum are taken and subsequently compared, the 
investigation for certainty of result is only a matter of 
time and trouble. 

I ought to mention that we tried in the case of the 
spark spectra (but without advantage) tinted collodion, 
with a view to work more towards the red end. The 
tinting substances used were Magenta, Judson's Violet, 
Annatto, Saffron, Turmeric, and Chlorophyll. Dr. 
Huggins' success in stellar photography with Iceland 
spar prisms promises a considerable extension of the 
spectrum in the ultra violet direction, and some recent 
investigations of Captain Abney and others work in the 
direction of the yellow and red regions, so that there 
is good hope of obtaining at no distant date a wide 
range of photographs including aU of the visible 
spectrum, and more. Of what assistance such faithful 
light pictures would prove to science, I need not here 
point out, except as an apology for our present attempt 
to popularise a subject hitherto somewhat of a sealed 
book confined to the laboratories of workers in special 




First Print. The Scale, — The scale has been already 
referred to in the Introduction. The photographs of 
the metals are so masked that in general when the 
scale is applied to them, it falls in its right place or 
very nearly so. To enable, however, the scale to be 
applied with greater exactness two fiduciary marks or 
points are indicated upon it, the one a bright line 
marked ' spark ' situated between h and F, the other a 
set of seven carbon or point lines between G and h 
marked ' arc' For the spark spectra the scale is ad- 
justed by applying the bright line marked ' spark,' to 
the bright line which appears prominently at the left 
hand of each spark spectrum. To adjust the scale for 
the arc spectra the set of lines marked ' arc,' are to be 
applied to the corresponding set of lines which are to 
be distinguished in most of the arc spectra towards the 
violet end, and which are the principal ones derived 
from the points and are considered as carbon or carbon 
compounds. Two prints are given of the scale, one on 
Plate I., and the other on Plate XXI., so that if direct 



application and comparison are desired one of them may 
be cut out and used for the purpose. 

Second Spectrum. Air with wide slit. 

Third Spectrum. Air with fine slit. 

These two spectra may be described at the same 
time. They differ only in length of the spark (which 
was taken between platinum points) and width of the 

The lines comprised in them may be traced more or 
less throughout all the spark spectra, and form useful 
indices for position of metal lines. 

Lecoq de Boisbaudran gives [Spectres Lumineux, 
Plate II., Etincelle longue], a spectrum comprising 
hues (with others) 5003, 4805, 4706, 4648, 4633, 
4449, 4434, 4347, and a band at 4240. This spectrum 
resembles generally our present spectrum, though it 
fails to agree in some respects, probably from the in- 
troduction of the condenser in our case. Our spectrum 
is for the stronger lines, identical with that of the hne 
spectrum of the capillary part of a nitrogen tube. {See 
Plate XXV. Fourth Spectrum). 

Fourth Spectrum. Arsenic Spark. — Small rough 
lumps of the metal placed in the clips. Spark white, 
and striking with ease across a considerable distance. 
Slight fumes of oxide at first, exposed twenty minutes. 
Two plates taken which were strictly identical, each 
showing the fiizzy bands on the margin of spectrum 
midway between F and G from about 4575 to 4475, 
and the lines in the bright part of the spectrum about 
4400, 4355, and 4310. Dr. Watts, in his ' Index of 


Spectra,' does not continue the spectrum of Arsenic 
beyond 5324 towards the violet ; but faint lines are, 
given on Huggins' authority, at 4551, 4537, 4497, a 
stronger one at 4464 and faint ones at 4369 and 4335. 


First Spectrum. Aluminium Spark. — Pieces of the 
metal in clips. Spark moderate in length, ten minutes 
exposure ; also tried with condensing lens in front of 
slit. Sht rather wide. 

Second Spectrum. Aluminium Arc, — Piece of 
metal cut from small bar, in carbon cup. Arc short, 
slit fine. 

Principal line in the spark spectrum at about 4500. 
This is represented in the arc by the edge of one of 
three sets of shaded bands. 

The two very conspicuous lines in the arc, between 
ff and H'^, are only represented by one near H^ in the 
spark. The edges towards the violet of the shaded 
bands in the arc are given by Lecoq de Boisbaudran 
[Plate XV., Aluminium metallique], at 4845, 4652, and 
4478. And the intense lines between H^ and H^ at 
3962 and 3943, (H^ is given in Watts' ' Index ' at 3968 
and IF at 3933). 

Third Spectrum. Antimony Spark. — ^Eough ] umps 
of metal in clips. Spark bright and broad. 

Fourth Spectrum. Antimony Arc. — Small pieces 

of metal in carbon cup, arc of moderate length, much 

oxide formed. 

c 2 


The spark spectrum is peculiar owing to the stream 
of light running along each margin of the spectrum, 
apparently thickening at each extremity, not only the 
metal, but also the air lines. Some of the air lines 
however escape ; proving that the appearance has not 
to do with the slit, but must be caused by metallic 
vapour hanging about each pole. (See also Lead and 
Antimony, Plate X., Fourth Spectrum.) 

The arc spectrum gives little beyond the point 
lines. We took several plates, but always with the 
same result in this respect. The lines given by Lecoq 
de Boisbaudran, [Plate XXTTT., Proto-chloriu-e d'An- 
timoine], are 5037, 4947, 4877, 4787, .4711, and 
Dr. Watts continues with 4693, 4588, 4349, and 4264. 
(See Lead and Antimony before referred to, where the 
lines are somewhat more distinct.) 


First Spectrum. Bismuth Spark. — Pieces of the 
metal in each clip, exposed ten minutes, spark bright. 

Second Spectrum. Bismuth and Nickel Spark. — 
Pieces of metal in clips, exposed ten minutes, current 
reversed at half. Note extension of metal lines in the 
middle of the spectrum, in consequence of breaking 
away of the point. 

Third Spectrum. Bismuth and Tellurium Spark 

Pieces of metal in clips, exposure ten minutes, current 
reversed at half. Tellurium partly fused, spark struck 
over Tellurium to the clip, (notice some iron lines from 


the clip projecting beyond centre of the spectrum at 
Tellurium pole). 

Fourth Spectrum. Bismuth Arc, — Piece of metal 
in carbon cup, arc moderate. 

The spectrum of bismuth with spark obtains easily, 
and the lines are well marked, those in the centre of 
the spectrum widening out considerably and showing 
in strong contrast to the air lines. 

Lecoq de Boisbaudran gives (Plate XXII., Chlorure 
de Bismuth), 5209, 5144, 5123, 5049, (4965, 4882), 
4724 (characteristic), 4303, 4259, 4118 (characteristic). 

Most of these lines appear in our spark spectrum, 
with others in addition. 

The principal lines in our arc spectrum are about 
4750 (very bright), and 4120 (probably Boisdaudran's 
4118). The vivid lines in the bright part of the spark 
spectrum do not appear in the arc. 

As to the second spectrum (Bismuth and Mckel), 
Lecoq de Boisbaudran gives [Plate XIX., Chlorure de 
Nickel], lines at 4873, 4867, 4856, 4832, 4808, 4788, 
4762, 4755, 4732, with principal ones at 4715 and 
4401. Our spectrum extends more into the violet, and 
shows a very bright line near H^ 

The Tellurium spectrum will be referred to in its 
order further on, 

PLATE 17. 

First Spectrum. Barium Spark, — Small pieces of 
metal in the clips which fused away rapidly, spaik 


bright. Spectrum peculiar as containing so little trace 
of the air lines, and for the fuzzy expansion of the 
principal lines. The lines generally are not confined to 
the margin, but cross the spectrum. Lecoq de Bois- 
baudran (Plate Vli., Chlorure de Barium dans le gaz) 
gives bands at 4974, 4873, 4794, and a barely visible 
line or band somewhat beyond. Dr. Watts gives bright 
hues or bands 4934, 4898, 4553, 4524, and 4130. 
From an examination of these last, I think that our 
spectrum (for want of the air lines) has been some- 
what wrongly positioned. 

If the Scale be advanced a httle to the right, so 
that the second bright hne in the spectrum coincides 
with 4898 (4900) on the Scale, the other Unes will be 
found to fall fairly into their places, in accordance with 
Dr. Watts' figures. 

Second Spectrum. Beryllium (Glucinum) Arc. — 
Metal in powder in carbon cup. Arc short. Dr. Watts 
gives two bright lines for Glucinum, 4572 and 4488. 

These are not prominent in our spectrum, which is 
chiefly characterised by the bright hues between ' spark ' 
and F, and by other fine lines scattered through the 
spectrum. The spectrum, however, bears so great a re- 
semblance to meteoric iron and meteorite (Plate X.), 
that there was found reason to suspect iron as form- 
ing the principal part of it. Upon testing the metal 
powder, it was found to contain iron as an impurity 
in considerable quantity. 

Third Spectrum. Boron Arc. — Graphitoid in car- 
bon cup. A dense glass-like crust of oxide formed 


on the upper carbon, which interfered with the current, 
and had to be frequently cleared off. Arc short and 
uncertain. The evidence of the spectrum is mainly 
towards the red end, where absorption bands seem 

FouETH Spectrum. Calcium Spark. — ^Pieces of 
metal in the clips inclined to fuse quickly. Spark 
fairly bright. This failed as a Calcium spectrum. The 
principal lines, a double one at about 4935, and others 
at about 4830, 4750, 4710, and 4060, are those of zinc. 
Upon testing the specimen of the metal, zinc was found 
present in considerable quantity. 


First Spectrum. Cadmium Spark. — Small pieces 
of the metal in clips, exposure moderate, plate rather 
weak, but clear of air lines. 

Second Spectrum. Cadmium Arc. — Pieces cut 
from small bars in carbon cup. Clouds of yellow oxide 
formed. Arc moderate. Metal burnt away quickly, 
Lecoq de Boisbaudran [Plate XX., Chlorure de Cad- 
mium], gives principal lines at 5085, 479 ), 4677, and 
a moderate one at 4414. 

These three principal lines appear in our arc 
spectrum, with an additional conspicuous line about 
4060. A line inflated at each end also appears at about 
4425 in the spark spectrum, which may be Lecoq de 
Boisbaudran's 4414. 

Third Spectrum. Arc between Carbon points. 


Fourth Spectrum. — A paper print from the plate 
of Spectrum 3, with all the lines which could be in 
any way seen on the glass negative ruled out. 

A description of the preparation of the carbon 
points has been already given in the Introduction. 
The Third Spectrum is an example of the plates ob- 
tained from the points alone. This plate contains, 
besides those that show in the print, a number of very 
faint hues seen only when it is held up to the light. 

A good paper print was obtained from this plate, and 
on this was ruled out all the hues that could be traced 
on the negative. A reversed copy of this is shown 
in the Fourth Spectrum. The lines are presumably 
those arising from the points, and a peculiarity of oiu: 
arc spectra in general seems to be that while these 
lines are all more or less present in each arc spectrum, 
the number and intensity differ much. They appear 
also to depend for number and intensity, to a con 
siderable degree, upon the metal or other substance 
burning in the arc, so that spectra of the same metal 
almost invariably contain, in addition to the metal lines, 
point lines of the same extent and character. It is this 
fact that seems to give to each spectrum its individuality 
referred to in the Introduction. 


FrasT Spectrum. Spark in Coal Gas. — ^For this 
spectrum the same spectroscope was employed as in 
the case of the metals. A glass tube with a bulb 


blown in the centre, of the form here shown (^ size), 
with platinum wires fused into the bulb was selected 


to pass the spark through. One end of the glass tube 
was connected, by means of elastic tubing, with the gas 
jet in the room. The other end of the tube was also 
joined to tubing which conveyed the gas out of the 
room into the air, after passing through the bulb. 
The two platinum wires were connected with the large 
coil and condenser, and while the spark was striking 
across the bulb (vertical with the slit) a current of 
coal gas at ordinary pressure was kept flowing through 
the tube. The spark was bright and slightly blue in 
tint. Carbon was soon deposited on the bulb. The 
spectrum shows a set of carbon hues, the two brightest 
at about 4580 and 4220, and also the hydrogen line 
h considerably expanded. This last line also has the 
appearance of being either double, or reversed, in the 
centre. The line 4220, and its accompanying group of 
fine lines on the right, occupy about the same place as 
a set of bright lines in the arc spectrum. They are 
however not identical, the lines in the coal gas diminish- 
ing in distance from each other towards the bright line, 
while in the arc the lines diminish towards the violet, 
(see a better enlargement of this negative on Plate 


XXVI., Second Spectrum). It is curious that we ob- 
tained this sharp line spectrum on only one occasion, 
though we subsequently took several other plates under 
similar conditions of apparatus and spectroscope. 

In the subsequent plates the line 4580 was replaced 
by a misty band, with a double or reversed appearance 
similar to the hydrogen line in our plate. Of its 
accompanying set of lines towards the violet, one 
only, the detached one nearest to the violet, remained. 
Line 4220 nearly disappeared, and remained only 
misty and indistinct ; while the group lines accompany- 
ing it were quite gone, and a bright broad band reach- 
ing to the hydrogen line took their place. 

The hydrogen line h was not so much expanded as 
in our spectrum, and a continuous spectrum crossed by 
two narrow bands or broad lines, and two other faint 
lines (Hydrogen?) appeared beyond it towards the 
violet. See also a plate of the same spectrum taken 
with the gas spectroscope C, Plate XXVIL Second 
Spectrum, and a print from the original plate, from 
which the present enlargement was made, Plate 
XXXIII. Fourth Spectrum. 

The plates of the subsequent spectra before de- 
scribed were altogether more misty and less defined 
than our first spectrum. 

Second Spectrum. Chromium Arc, — Metal powder 
in carbon cup, some scintillation during combustion. 

Lecoq de Boisbaudran gives [Plate XVI., Sesqui- 
chlorure de Chrome], a very bright line at 5205, a 
double one at 4649, a band of indistinct rays at 4343, 


and three well-marked lines at 4290, 4275, and 4255. 
The line 5205 does not appear in our spectrum, (the 
outside line towards the red is a carbon one). The 
other Unes are easily distinguished. 

A set or band of close lines is also to be noticed at 
about 4540. 

Thied Spectrum. Cobalt Arc. — Small piece of 
metal in carbon cup, arc moderate. Lecoq de Bois- 
baudran [Plate XIX., Chlorure de Cobalt] gives a list of 
twenty-one Hues in the part of the spectrum comprised 
in our photograph, distinguishing for brightness 4868, 
4840, 4815, and 4533. In our spectrum the lines show 
pretty much of equal intensity, and it is somewhat diffi- 
cult to separate them from the carbon lines. 

Fourth Spectrum. Copper Spark. — Small pieces 
of wire, spark tinged green, spectrum poor, principal 
line crosses a part of the air spectrum deficient of bright 
lines, at about 4280. 


First Spectrum. Copper Arc. — Stout pieces 
of copper wire used as terminals, arc narrow, brilliant 
green in tint and of moderate length. 

Second Spectrum. Copper Arc. — Small bead of 
prepared wire, an aUoy of gold, silver, and copper in 
the carbon cup. The wire was prepared by a jeweller 
as an equal part alloy of pure gold and silver, but it 
subsequently proved that the gold was adulterated with 


{Note, — ^The images of these two spectra are not 
of the same actual size, the carbon arc being some- 
what the larger, and allowance must be made for this 
in comparing them with each other and with the 

In the case of the alloy, the copper, though so inferior 
in quantity, seems to have mainly appropriated to itself 
the spectrum. The gold and silver lines are very faint, 
but they may be traced by comparison with the spectra 
of these metals. (See also Plate XV., Spectrum Silver 
and Copper Arc, where copper again monopolises the 

Most (but not all) of the lines in the First Spectrum 
appear in the Second Spectrum, mixed with a few of 
the principal carbon or point lines. The bright single 
line about 4400 in the first spectrum appears double 
in the second spectrum. 

The very conspicuous double line in the first 
spectrum at about 4075 is replaced by a single bright 
one, with faint companion in the second. 

Lecoq de Boisbaudran gives [Plate XXIV., 
Chlorure de Cuivre en solution], a long list of copper 
lines, including the three characteristic ones (5218, 
5153, and 5106), seen on the extreme left of our 

He also gives on the same plate the spectrum of 
Chlorure de Cuivre dans le gaz, with brighter groups 
towards the violet. These spectra do not in general 
character accord with ours. 

Thied Spectrum. Didymium Arc, — ^Powder in 
carbon cup, arc short, spectrum full of many coarse 


lines of the same character; with traces, especially 
towards the red and the centre, of absorption bands. 
The carbon lines are either absent or so obscured by 
the metal spectrum as almost to cease to serve as 
guides in masking. Lecoq de Boisbaudran gives [Plate 
Xin.] two absorption spectra of Didymium, neither of 
which readily compares with ours in lines or character. 

Fourth Spectrum. Erbium Arc. — ^Powder in 
carbon cup, a bead of the fused metal insisted on 
adhering to the negative pole, the arc being then longer 
than when the metal remained in the cup. When the 
metal was burnt in the cup the arc was brightest. 
The spectrum is characterised by a considerable number 
of bright lines, with many very fine ones between ; the 
carbon lines are also in this case either absent or very 
much obscured, so that position on mask is doubtful. 
Lecoq de Boisbaudran gives [Plate XIV.] a spectrum of 
* Erbium emission,' which does not assist in examining 
ours. Dr. Watts gives a joint spectrum of Erbium and 
Yttrium, with some lines common to both metals. Our 
spectrum of Erbium does not accord with that of 
Yttrium, Plate XIX., in lines or general character. 
We found in our cabinet, a specimen labelled Terbium, 
of which we also photographed the spectrum. On 
comparing it with oiu- present spectrum of Erbium, 
(except that the one spectrum has a little less glare 
than the other) the two spectra were found absolutely 
and line for line coincident. 

Every line is exactly repeated in each plate, and the 
relative intensities of the lines are preserved in each 
spectrum in the most accurate manner. 



First Spectrum. Gold Arc, — Small lumps of metal 
in the carbon cup. Arc short. Spectrum fairly clear of 
point lines. Lecoq de Boisbaudran gives [Plate XXVI. 
Chlorure d'Or en solution] lines at 5063, 4812, 4793, 
4608, 4490, 4437, 4338, 4314, 4064. The lines 4812 
and 4064 are recognised in our spectrum, as also a 
strongish line about 4570. 

Second Spectrum. Indium Arc. — Small piece of 
the metal cut from bar in carbon cup, arc moderate, 
spectrum with a good deal of glare, point lines indis- 
tinct. Two principal broad and expanded metal lines 
read off at about 4515 and 4100, (Lecoq de Boisban- 
dran gives Plate XXI., Sels dlndium, 4511 and 4101). 
For spark spectrum of Indium, see Plate XVI., Third 

Third Spectrum. Indium Arc. — ^Piece of metal in 
carbon cup. Arc short. Spectrum bright. Point lines 
long in centre. Note group of very fine lines at ex- 
treme left towards the red, (centre about 4990) with 
two dark spaces to right of them, also two bright lines 
about 4550. Dr. Watts gives a spectrum of * Iridium, 
and Euthenium,' with lines (Kirchhoff) 6347, 5449, 
and 5299. For our spectrum of Euthenium, see 
Plate XTV"., Second Spectrum. The two spectra 
certainly have a very close general resemblance. Note 
the group of four lines towards the red end and the 
outlying short line at the extreme violet end, common 
to both. 


Fourth Spectum. Iron and Copper Spark, — Wires 
of the metals in the clips, condensing lens, in front of 
slit, slit wide. Image rather coarse. Iron lines pro- 
jecting in several places beyond the upper edge of the 
specflrum. Copper line at about 4280 seen projecting 
on lower edge of the spectrum. 


First Spectrum. Copper and Iron Spark, — Same 
as last (Iron and Copper), but metals reversed in chps, 
no condensing lens, slit wide and image confused, but 
lines can be traced through the glare. 

Second Spectrum. Iron Arc. — Eeduced powder 
in carbon cup. Arc moderate, much scintillation. 
Thirty cells Grove only used, sKt rather wide. Spec- 
trum imperfect, but introduced to show how battery 
power may vary general aspect of the spectrum. Note 
broad dark space about centre of spectrum, also glare 
of light towards the red, with group of lines at ex- 
tremity of spectrum in that direction. 

(This spectrum is not positioned to the. Scale, but 
can easily be compared by eye with the next). 

Third Spectrum. Iron Arc. — Eeduced powder in 
cup forty cells Grove. Slit fine. Spectrum much more 
uniform than last, point lines absent or indistinct. 

Lecoq de Boisbaudran gives [Plate XVIII., Per- 
chlorure de Fer en solution Etincelle] a spectrum com- 
prising a set of groups of lines in the violet separated 
from those at the other end of the spectrum by a 


blank space. This blank space is also seen in our 
photograph separating the four characteristic lines to- 
wards the red end of the spectrum from the main body 
of lines towards the violet. 

The lines towards the red in our spectrum evidently 
correspond with Lecoq de Boisbaudran's 4959, 4923, 
4891, and 4874. Our spectrum is slightly out of 
position on the mask ; but if the scale be moved a 
little towards the left, so that the first of the set of 
these four lines be made to coincide with 4959 on the 
scale, most of the other lines in Lecoq de Boisbaudran's 
list may be picked out. 

Fourth Specteum. Iron and Selenium Spark. — 
This spectrum is introduced to show the iron lines in 
spark. Two small pieces of Selenium were placed in 
the steel clips. When the spark passed, in lieu of 
striking from pole to pole, it flew with a long and 
bright flash across the surface of the selenium melting 
it in its way. 

On examining the spectrum, it was found a com- 
bined one of air, selenium, and iron, some of the lines 
of the latter projecting in a most marked manner be- 
yond the edges of the spectrum. These lines were 
evidently due to the clips. We tried Selenium two or 
three times, and always with the same result as to 
behaviour of the spark. 

Now and then it seemed to cross between the poles, 
but ordinarily it preferred the longer route across the 

The Spectrum of Selenium will be found referred 
to in its order further on. 



First Spectrum. Meteoric Iron Arc. 

Second Spectrum. Meteorite Arc. 

Three specimens purchased of Mr. James E. Gregory 
were used m the arc : — 

No. 1. Meteoric Iron. Atacanna 1827. 

No. 2. Meteoric Iron. Tolucca 1784. 

No. 3. Piece of Meteorite. Ausson 1858. 
They all burnt with much scintillation in the car- 
bon cup. The spectrum of No. 1 when examined was 
found identical in all respects with the spectrum of Iron 
in arc (third spectrum, last plate) and might have been 
taken for the same photograph. 

No. 2 and No. 3 (the plates which are printed) also 
gave spectra evidently of iron, but differing from the 
spectra of No. 1 and of Iron in arc in last plate and 
from each other. Each of th^m is characterised by 
the large number of sharp and fine lines, which more 
especially in the case of the meteorite, intermediately 
fill up and occupy nearly the whole spectrum. Some 
of these lines it is true may be traced very faintly in 
our spectrum of Iron on Plate IX., but they appear to 
come out relatively stronger and brighter in our present 
plates. Meteorite seems also to differ from meteoric 
Iron in the greater length of spectrum (note group of 
fine lines to the extreme left), and in the greater 
number of its fine lines generally. This will be par- 
ticularly noticed about the brighter and wider part of 



the spectrum where the coarse and strong lines 
mainly prevail. Some of these, which have dark in- 
tervals in the case of meteoric Iron, are connected by 
and filled up with fine hues in the case of meteorite. 
Note also a thick double line about 4048 in meteorite, 
which is doubtfully represented in the meteoric Iron 

Third Spectrum. Lead Arc. — ^Piece of metal in 
carbon cup. Arc moderate. 

Fourth Spectrum. Lead and Antimony Spark, — 
Small lump of antimony in one clip; small bar of 
lead in the other. Current reversed at half exposure. 
Lecoq de Boisbaudran gives [Plate XXTTT., Plomb 
m^tallique Etincelle] lines at 5044, 5003, 4386, 4245, 
4167, 4056, noting 4056 as very characteristic. Lines 
appear in our arc spectrum corresponding with his 
5003, 4386 (4245 and 41()7 are mixed up with the 
point Unes) and very prominently indeed 4056. We 
have lines also about 4825, 4750, and 4700, which he 
does not give. In the spark spectra we get prominently 
Boisbaudran's 5044, a bright line about 4780, a tre- 
mendous one at ,4400, another still larger at 4250 
(Boisbaudran 's 4245 ?), and lastly 4056, very sharp 
and well defined. 

The wonderful inflation and flare of the two lines at 
4400 and 4250 are to be noted. In the case of the 
latter line the flare appears unequally towards the 
violet side. Other smaller lines are in the spectrum 
(see Magnesium and Lead, second spectrum on next 


The Antimony Spectrum has been already described, 
but note the glare of light and thickening of the lines 
before referred to in reference to that spectrum. 


First Spectrum. Lead and Magnesium Spark, — 
Small bar of Lead in clip ; Magnesium ribbon cut to a 
point in other clip. Current reversed at half time. 

Second Spectrum. Same as above, except that the 
metals are reversed in position. A condensing lens 
was used in front of slit. 

Third Spectrum. Magnesium Spark. — A piece of 
magnesium ribbon, cut to a point, used in each clip. 
Slit '001 inch. Exposure fifteen minutes. 

Fourth Spectrum. Magnesium Arc ^Piece of 

ribbon coiled up in the carbon cup, quickly ignited, 
and long arc obtained ; much oxide formed. 

Lecoq de Boisbaudran gives [Plate XII. Chlorure de 
Magnesium] lines as follows : group, 5183, 5172, 5167, 
very bright (6 in solar spectrum), then a band of rays, 
commencing with 5006 and ending with 4958, and 
then single lines, 4705 and 4483. 

Our first two spark spectra are mainly conspicuous 
for the great blaze of light at about 4500. This is 
very marked and characteristic, and extends in each 
case considerably beyond the margin of the spectrum. 
In our third spectrum (Magnesium ribbon in each clip) 
the print is cut off in vertical by the limited width of 
mask ; but upon examining the original plate the glare 

D 2 


of light on the lower margin of the spectrum at 4500 
is distinctly traced to extend beyond the margin of the 
spectrum to a length equal to the glare itself (nearly 
half the width of the spectrum) as a single hne ter- 
minating in a minute knob or inflation (limit of prism 
surface ?). Two bright lines at about 4725 (Boisbau- 
dran's 4705 ?) and 4360 are also seen to project 
beyond the spectrum, though not to so great an extent. 
Both of these last lines appear to be repeated in the 
arc spectrum, while the large 4500 is missing there. 
The group b in solar spectrum is seen in both spark 
and arc spectra as a double line only (tested by this, 
our Scale is a little too much extended towards the 
extreme left). Then in the arc comes the band of 
lines at 5006, then 4725 and 4360, and lastly two 
bright lines at about 4245 and 4180. The other and 
fainter lines in the arc seem due to carbon. 


First Spectrum. Manganese Arc, — Powder metal 
in the carbon cup ; arc moderate, with some scintil- 
lation, taken with battery of 30 Grove cells. 

Second Spectrum. Same, but taken with battery 
of forty Grove cells. Lecoq de Boisbaudran's Plate 
XVn., Chlorure de Manganese en solution, Etincelle 
courte, is found closely to compare with our spectrum 
in principal lines, and the two spectra were selected to 
form a scale by comparison and interpolation as 
described in the Introduction. The lines given by 


Boisbaudran are 4825, 4784, 4766, 4755, 4738, 4727, 
4710, 4502, 4462, 4437, 4415, 4282, 4266, 4260, 
4237, 4084, 4063, 4047, 4039. These were also com- 
pared with Dr. Watts' list of (Huggins') lines of Man- 
ganese ; and then those most easily recognised with 
corresponding ones in our spectrum were used as 
materials for the Scale. The principal lines are easily 
sorted out by the aid of the upper spectrum. 

Third Spectrum. Mercury Spark. — Globule of 
the metal in a small glass cup with Platinum commu- 
nication passing tlirough the bottom of the cup. 
Platinum wire electrode above. Exposure twenty 
minutes. Spark brilliant and rapid. 

The spectrum is characterised by the misty and 
indistinct appearance of the air hues. They are, how- 
ever, sufficiently defined to indicate position of the 
metal lines, these last being coarse and thickened. 
Lecoq de Boisbaudran gives [Plate XXV., Bichlorure 
de Mercure] a strong line at 4357, and two other lines 
at 4078 (faint), and 4047 : 4357 is well marked in our 
spectrum, also 4047, and there is an additional strong 
line at the end of the spectrum about 3985. 

Fourth Spectrum. Molybdenum Arc, — Powder 
metal in carbon cup. Soon formed a bead, which re- 
mained quiet at bottom of the cup. Arc long, and 
gave a bright lambent glow rather than a brilliant 

Dr. Watts gives hues (Thalen), 4979, 4867, 4829, 
4818, 4757, 4730, 4706, 4536, 4475, 4433, 4411, 
4380, 4326, 4277, 


The group 4737, 4730 and 4706, is easily dis- 
tinguished, and other of the foregoing hnes may be 
picked out in the clearer parts of the spectrum. 


FiKST Spectrum. Nickel Arc. — Small pieces of metal 
in the carbon cup, arc short, spectrum tolerably clear 
of point lines. Leccq de Boisbaudran gives [Plate 
XrX., Chlorure de Nickel] a long hst of hnes com- 
mencing with a strong one 4984, and ending at 4288, 
and with characteristic ones at 4715 and 4401. 

4715, 4647, 4606, 4550, 4461, and 4401 (strong), 
may be picked out in the clearer part of our spectrum 
towards the red end. Notice also a sharp bright line 
in a clear space about 4000. 

A small bottle without a label containing a powder 
was found in our cabinet. The spectrum when photo- 
graphed was at once easily identified with our present 

Secoist) Spectrum. Niobium Arc, — Powder metal 
in carbon cup, arc moderate. Dr. Watts quotes 
Thalon as stating that the lines of Niobium are too 
faint to be measured satisfactorily. 

Our spectrum, however, after excluding the carbon 
lines has a considerable set of bright ones which must 
belong to the metal. These may be seen at about 
4861 (F), 4615, 4590 (strong double), two bright lines 
with a fine one between them about 4435 and 4405, a 
set of three lines, (a single and then a double) about 


4260, a bright one with shading towards the violet, at 
4100 (A), (it is curious that F and h places of 
hydrogen lines should each have prominent lines 
falKng in the same or very closely approximate 
positions in this spectrum), a thickened or double line 
about 4050 (position also of a carbon line), and a 
double one near to the last about 4040. 

Third Spectrum. Palladium Arc. — Piece of metal 
in the carbon cup, arc moderate, spectrum showing 
carbon lines indistinctly. 

Lecoq de Boisbaudran gives [Plate XXVIL, 
Chlorure de Palladium,] a set of lines at 5118, 5114, 
and 5111, then single lines at 5063, 4969, and 
4917, then three well-marked lines at 4874, 4818, 
and 4788, then one at 4475, then a strong one at 4214, 
concluding with two at 4170 and 4088. The hues at 
5111 and 5063, and the stronger ones at 4874, 4818, 
4788, 4475, and 4088, may be all picked out from our 
spectrum. A carbon line between H^ and H^, seems 
also to have another by its side not belonging to it. 
Note also extension of spectrum towards the violet, as 
in the cases of Iridium and Euthenium. 

Fourth Spectrum. Platinum Arc. — Small roll of 
foil in the carbon cup, arc short, spectrum poor, 
mainly carbon lines. Lecoq de Boisbaudran gives 
[Plate XXVII., Chlorure dePlatine] a set of lines com- 
prising (with others) 4554, 4524, 4501, 4415, 4390, 
4118. These seem distinguishable in our spectrum, 
and there are also two bright lines about 4250, not 
given by Boisbaudran. 



First Spectrum. Rhodium Arc. — ^Kece of metal in 
the carbon cup. Spectrum of even character, with 
many sharp metal lines. Point lines not prominent, 
except in the centre of the spectrum, 

Here again Dr. Watts quotes Thal^n, that the lines 
are too faint to measure, but many may be picked out. 
from our print. Note especially two sharp hues 
between 5000 and 4950, a double line near F, a line 
about 4590 near two point hues, another about 4420, 
with two fine ones towards the red, and a strong one 
near a carbon line about 4100. Other lines will also 
be found, intermediate of the point lines, in the region 
extending from 4400 towards the red end of the 
spectrum. Note also a set of three lines (strongest 
towards the red), about 4265, and a strong set of three 
lines of equal intensity, the centre one about 4125. 
N.B. In this and other cases in which no authentic list 
of lines is referred to, it is useful to test the spectrum 
by the carbon points ruled out, Plate V., so as to 
eliminate the point lines from the spectrum. 

Second Spectrum. Ruthenium Arc. — ^Hece of 
metal in the carbon cup, arc short. This spectrum has 
already been referred to under the head of ' Iridium.' 

Third Spectrum. Selenium and Tellurium. — 
Small piece of these in each clip, current reversed 
at half. 

Fourth Spectrum. Selenium and Aluminium. — 
Small piece of Selenium in one clip. Aluminium 


wire in the other, current not reversed. The Aluminium 
spectrum, Plate II., has been described ante^ p. 19. It 
is, however, from the absence of air hues, well shown 
in the present print. See also Plate XVII , Second 
Spectrum, Titanium and Aluminium. The spark passed 
more freely than when both electrodes were of Seleniiun, 
but still played over the surface of the Selenium partly 
fusing it. (Compare Iron and Selenium Spark, Plate 
IX., and note the Iron lines in each of the present 
spectra as affecting the Selenium pole of the spec- 

In the third spectrum the Selenium has partly 
melted away, and the spectrum is doubled. 

The spectrum of Selenium is distinguished by its 
quantity of very fine sharp lines towards the red 
running into bands towards the violet. Many of these 
lines in our plates are too fine to print satisfactorily. 
The lines are best seen in the spectrum Iron and Sele- 
nium, Plate IX., the bands in our two present plates. 

In each case the metal Unes and bands follow 
the ordinary rule of being found at the edges of the 
spectrum. There is an inclination to mistiness or glare 
at the poles, as in the case of Antimony. Dr. Watts 
gives from Pliicker a long list of close lines towards the 
red end, and of bands towards the violet end of the 

We pick out conspicuously in our spectrum bright 
lines at about 5000 (Plucker's 4994 ?), 4850 (Plucker's 
4845 and 4840?), 4880 (Plucker's 4776?), 4600 
(Plucker's 4606 ?), and 4425. The bands towards the 


Violet are also well seen about 4225, 4190, and 4140. 
The two sharp lines about 4015 and 3998 are Iron 


First Spectrum. Silver Spark, — Small bars of the 
metal in clips. Spark short and white, edged with 
greenish glare. Exposure twenty minutes. 

Second Spectrum. Silver Arc ^Piece cut from 

bar of the metal in the carbon cup. Soon became red 
hot, and melted into a bead, which rotated in the cup, 
and from which the arc sprang. Arc moderate, and 
tinged with green. 

Lecoq de Boisbaudran gives [Plate XXV., Azotate 
d' Argent en solution] a set of lines commencing with 
two very strong ones at 5464 and 5208, a band or set 
of lines at 5022, 4997, 4968, and following on with 
4669, 4622, 4570, 4518, 4475, 4434, 4396, 4208. 

In our spark spectrum we have in our plate a line 
about 5150, which has not printed. 4997 seems indi- 
cated by the breadth and strength of the ' spark ' line. 
Four air lines, 4960 to 4900, are unusually strong. 
4669 is marked by projecting slightly beyond the 
spectrum. The other lines do not show. The battery 
and coil power does not seem to have been sufficient 
to bring out the metal lines satisfactorily. In our arc 
spectrum we find brilliant lines corresponding with 
5208 (our Scale, as we have noticed before, is a little 
too much extended towards the red in this part of it). 


4690 (Boisbauclran's 4669?), 4480 (his 4475?), and 
two very strong lines, about 4215 (i)lace of a point 
line), and 4050. 

Third Spectrum. Silver and Copper Arc. — A 
small piece of metal wire in the carbon cup. This was 
procured from a jeweller, and warranted pure as 
being the silver wire employed by the natives of India 
in making filagree and other ornamental work. It had, 
however, I thought, a shghtly reddish tint, and upon 
combustion (behaving much the same as the last spe- 
cimen) the spectrum proved a mixed one of copper and 

For some reason which we do not trace, the 
spectral image is smaller in size than that of Silver arc. 
The enlargements are both once, and the difierence is 
in the original plates. It is however almost exactly 
the same size as Copper arc, first spectrum, Plate VII. ; 
and this last can be used to distinguish the copper hues 
in our present spectrum. They mainly usurp the spec- 
trum, but the Silver line at 5208 (apparently doubling 
the copper line 5218), and those at 4215 and 4050, 
are easily recognised. 

Fourth Spectrum. Solar Spectrum, — This spec- 
trum was photographed mainly for the purpose of 
comparison with the metal spectra in regard to the 
dispersion of the spectroscope, but also as a sort of 
check upon our Scale, see Plate XXI., Scale and Solar 
Spectrum. The solar lines are fairly seen, but they are 
too fine and close together, and on too small a scale to 
make them available for comparison with the coarser 


metal lines. Indeed, this comparison did not form 
part of our intended work. The photograph was 
taken on a fine, but not absolutely clear, day in winter 
with the sun near the meridian. A table was arranged 
in the open air, facing the south, with the spectroscope 
and camera as used for the metals upon it, the photo- 
grapher's back being to the sun. The slit was made 
as fine as possible, and a plane mirror and condensing 
lens were used to throw the sun's image in a parallel 
direction upon it. The slit was covered with a cap, 
which was removed when it was desired to take the 
photograph. Of the two successful plates, one was 
exposed three seconds, the other two seconds. The 
last has the lines sharpest and most distinct. This 
plate indeed is very sharp, and the lines are well de- 
fined ; but it is difficult to get as good an eflfect in the 

The lines in the plate are seen nearly as far towards 
the red as b. In the print they stop short midway 
between h and ' Spark.' F, G, and h are well marked. 
The print stops short at H ^ ; but in the plate a 
br'ght space with four dark lines succeeding H ^ is seen, 
and then the spectrum terminates abruptly with the 
dark interval representing W. 


First Spectrum. Strontium Spark. — ^Pieces of metal 
in the clips. Spark bright, metal melted rapidly. 
Spectrum (like Barium) characterised by the absence of 


air lines, and by the broad fuzzy character of the 
metal hnes. Lecoq de Boisbaudran gives [Plate IX., 
Chlorure de Strontium en solution] four lines (second 
and fourth the strongest) with places as follows : — 
4307, 4215, 4163, 4079. 

Assuming the first expanded line to be 4307, and 
placing the Scale accordingly, the other three lines 
4215, 4163, 4079, towards the violet, fall into their 
proper places. The bright unexpanded line towards 
the left of 4307 seems to be an air line. 

Second Spectrum. Tellurium Sparky (see also 
Plate XIV., Selenium and Tellurium Spark). — Eough 
pieces in each of the clips, which wore away 
quickly, the spark occasionally running to the clips. 
Spectrum characterised by comparative absence of air 
Knes and a general likeness to Selenium without its 
very sharp lines. Dr. Watts gives lines (Thal^n) 
4895, from his own observation 4866, 4832, 4785, then 
three (Huggins') 4709, 4664, 4652, then one of his 
own 4602, and then (Huggins') 4599, 4544, 4479, 
4352, 4302, 4259, 4063. In oiu: Spectrum, lines or 
bands are well traced between 4900 and 4650 in 
places nearly corresponding with some of the above, as 
also a band at about 4485 (4479 ?) and some bright 
bands in the margins of the lighted-up region 4350 to 

The line or band 4063 seems also recognisable on 
the lower margin of the spectrum. 

Third Spectrum. Thallium and Indium Spark 
(for Indium Arc, see Second Spectrum, Plate VIII.) 


— Small pieces of the metal in the clip, current reversed 
at halt^ spark bright. Spectrum characterised by 
absence of air lines, and distinctness of metal lines. 
On the print, seven lines belonging to Thallium may 
be counted. Two if not more, finer ones appear on 
the plate. Seven lines at least are seen on the 
Indium margin of the spectrum, including the large 
ones seen in the Arc Spectrum of Indium which, as 
in the case of the arc, are very sharp and well defined 
and run nearly across the spectrum. (This spectrum 
was originally a short image, and is also very slightly 
underenlarged so that the whole is slightly shorter 
than the Indium Arc Spectrum. Allowance must be 
made for this in placing the Scale.) 

Lecoq de Boisbaudran gives no lines for Thallium 
in our part of the spectrum, and only the two referred 
to ante for Indium. Dr. Watts gives for Thallium, on 
his own, Huggins', and Thal^n's authority lines at 5153, 
5085, 5078, 5054, 4980, 4945, 4893, 4767, 4737, 
4112. Our Scale indicates on our spectrum lines which 
correspond with 5153 (scale too much extended in that 
part), 5078, and notably 4767 (very bright and broad). 
A line is shown about 4300, and one about 4120 (4112?) 
is faintly indicated. Two lines appear in the plate 
about 4945 and 4893 which do not show in the print. 
Dr. Watts gives for Indium (Thalen) 5532, 4509, 
4101. Allowing for the difference in size of the 
toage before referred to, 4509 and 4101 are easily 
distinguished sharp and well defined and projecting 
beyond the spectrum ; 4532 is not definitely traced. 


but on each side of 4700 broad and bright hnes or 
bands are seen. Note also a bright line about 4090, 
with a faint one beyond. A shght flare seems to run 
along the Indium margin of the spectrum. 

Fourth Spectrum. Thallium Arc, — Piece of the 
metal in the carbon cup. Arc moderate, metal very- 
soon volatilised, and we doubted whether any trace of it 
was impressed upon the spectrum. A fine line at the 
extreme red end of the spectrum about 5250, and 
others about 4610, 4405, 4260, and 4100, are however 
intermediate of the point lines ruled out. They may 
be metal lines, but their character is not what one 
would expect in that case. 


First Spectrum. Titanium. Spark. — Two pieces of 
ore in the clips. Spark occasionally gave a reddish 

Second Spectrum. Titanium^ Aluminium^ and 
Palladium., — Palladium in clip, for upper pole. Lower 
pole a small Aluminium cup, (with Platinum wire let 
through the bottom) filled with Titanium in powder. 
Current reversed half time. Spark long and bright, 
and occasionally played round edge of the cup, fi:-om 
which some of the powder was from time to time 
ejected. Aluminium spectrum due to the cup very 
apparent on upper edge of spectrum in print. Air lines 
in first spectrum weak towards the red end. 

Third Spectrum. Titanium Arc, — Metal powder 


in the carbon cup. Soon formed a bead, which remained 
quiet in the cup. Arc long and lambent. 

Dr. Watts gives (with wave lengths by Thal^n) a 
long list of Titanium lines, most of them of considerable 
intensity, and in some parts of the spectrum very 
closely packed together. Between 5300 and 4163 we 
count no fewer than 149, the greater number being of 
the higher range in intensity. 

Our spectrum contains several groups of fine lines 
close together. One to the extreme left at about 
5025 to 4975. A wider set, about 4925 to 4850 ; 
another wide set, 4700 to 4625. A set of fine bright 
lines 4560 to 4525, and another set about 4390 to 
4340. Single bright lines are distinguished about 
4775, 4550, 4460. A set of five of about equal 
distance apart between 4450 and 4400, and a single 
one about 4300. The single ones may be Thal^n's 
4779, 4549, 4468, and 4299, the first being of Watts' 
intensity 6 and the three last his intensity 10. Going 
back to the spark spectra, we fail to trace much evidence 
of the metal lines. In the first spectrum the principal 
evidence of the metal is confined to a few sharp faint 
lines partly crossing the spectrum. 4549 is thus seen, 
and two others about 4420. 

The strong well-defined lines in the bright part of 
the Spectrum are Iron (hence the red flare in the 
spark). In the second Spark Spectrum no more is 
seen, the strong lines on the upper margin being those 
of Aluminium. 

Dr. Watts gives lines for Palladium (Huggins and 


Thal^n) 5062, 4876, 4818, 4787, 4474, 4278, 4212. 
In our spectrum 4876 is indistinctly traced, then a 
line thickened at margin about 4710, 4474 seems 
well marked. About 4300 is a conspicuous bright line 
projecting beyond the spectrum (4278?) with others 
near it. A bright Kne is well seen at 4225 (4212 ?) 
and another not so bright at about 4165. A faint line is 
also seen beyond H^ which may belong to the metal. 

Fourth Spectrum. Tin Arc. — Some granular 
metal in the carbon cup. Arc short, spectrum con- 
spicuous for a few metal lines and the brightness of the 
lines in the region of H^ and H'^. All the other point 
lines (except 4225) indistinct. Lecoq de Boisbaudran 
gives only one line in our part of the spectrum which 
is easily recognised, 4526 ; but note also a line about 
4100, which does not seem to be a point line, and which 
has the peculiarity of only partly crossing the spec- 


First Spectrum. Tin and Zinc Spark, — Small Zinc 
bar in one clip. Granular tin same as used in arc 
in small glass cup, with platinum wire connection for 
other electrode, current reversed at half, slit rather 

Second Spectrum. Tin and Zinc Spark, — Second 
plate of same. 

Dr. Watts gives for Tin (Thalen) 5100, 5021, 
4923, 4858, 4585, 4524, (Boisbaudran's 4526). The 
First Spectrum shows towards the red end 5100 and 



4923. Then referring to the second spectrum, we get 
4858, 4605 (4585?), 4550, 4540, and about 4515 
(4524 ?). The one bright hne in the arc (4524) is 
but faintly represented in the spark spectrum. 

Third Spectrum. Uranium Arc. — Powder metal 
in the carbon cup. Arc moderate, some scintillation. 
Spectrum much glared, with many indistinct rather 
coarse lines, from among which the point lines about 
H^ and ff and 4225 shine out conspicuously. Dr. 
Watts gives a set of lines (Thalen), among which 4472, 
4393, 4374, 4362, and 4340, may perhaps be selected 
in our spectrum. 

Fourth Spectrum. Vanadium Arc, — ^Powder 
metal in carbon cup. Arc moderate. A splendid spec- 
trum, characterised by a family likeness to Titanium, 
but with a yet greater quantity of bands of close sharp 
lines. Dr. Watts gives a list (Thalen) of thirty- 
two lines between 4881 and 4085 (about where our 
spectrum begins and ends). Groups of lines are found 
with centres about 4843, 4585, 4389, and faint lines 
extending from 4130 to 4085. This will be seen to 
very closely agree with our spectrum, in which the 
groups quoted (with others) stand out very beautifully. 


First Spectrum. Wolfram Arc. — ^Powder metal 
in carbon cup. Arc moderate. Spectrum somewhat 
like Uranium in character, but with brighter lines and 


Dr. Watts gives lines (Thalen) for Tungsten 5014, 
5007, 4981, 4887, 4842, 4680, 46G0, 4659, 4302, 
4295, 4269. Most of these may be recognised in our 

Second Spectrum. Yttrium Arc. — Powder metal in 
carbon cup. Spectrum well defined, point lines absent, 
notably those about H^ and ff and others generally 
seen towards the violet. Yttrium and Erbium are 
given as a combined spectrum by Dr. Watts, but our 
photographed spectra have little in common. 

Dr. Watts gives in our part of the spectrum, 4822 ; 
then two we do not find ; and then 4674, 4643, 4505, 
4422, 4397, 4374, 4357, 4309, 4236, 4227, 4176, 
4167, 4142,4127,4102. 4102 is very well marked, 
and if the Scale be adjusted to this line, many of the 
others may be picked out. 

Third Spectrum. Brass Arc, — Two pieces of 
stout brass wire. Arc did not form well. A mixed 
spectrum of Zinc and Copper, the principal lines of each 
metal being easily distinguished, the zinc lines towards 
the red end of the spectrum, the copper towards the 
violet end. 

Fourth Spectrum. Brass Spark. — Two points of 
brass wire as electrodes. Spark passed freely, spectrum 
deficient towards the violet, introduced to show the 
double zinc line about 4925. 

£ 2 



FiKST Spectrum. Zinc Arc, — Small piece of the 
metal in carbon cup. Arc brilliant. Much oxide 
formed. Lecoq de Boisbaudran gives [Plate XX., 
Chlorure de Zinc en solution] three brilliant Hues 4812, 
4721, 4681, and another not so strong at 4630. Dr. 
Watts gives (Huggins') faint lines at 5049 and 4970, 
two strong ones at 4924 and 4911, a faint one at 4867, 
and then three strong ones at 4809, 4722, 4679, 
(Boisbaudran 's 4812, 4721, and 4681). Compare the 
arc spectrum, the two tin and zinc spark spectra 
on Plate XVIII. and the brass spark spectrum on 
Plate XIX. 

Boisbaudran's 4812, 4721, 4681, and 4630, are all 
very prominent in the arc spectrum, together with a 
double one at the other end of the spectrum, about 
4060, (sed quaere a point line. It or a line very 
approximate occurs in other arc spectra). In the tin 
and zinc spark spectrum No. 1, 5049, 4924, and 4911, 
and 4809, 4722, and 4681 are seen without 4630. 

In tin and zinc spark No. 2 the three stronger lines 
alone are "seen, while in brass spark 4924 and 4911 
alone appear. 

Such effects are probably due in the case of a single 
metal to difference in strength, and temperature of 
spark or arc ; but in the case of mixed metals the effects 
produced, and the causes leading to them, seem to have 
a complication of their own. 


Second Spectrum. Zirconium Arc. — Thin flakes 
of the metal in carbon cup. Arc short and brilliant, 
thick coat of oxide formed, occasionally stopping the 
current and requiring pole to be cleaned ; slit fine. 
Spectrum characterised by three prominent shaded 
sets of bands or lines towards the red end. Dr. Watts 
gives (Thalen) five strong lines (intensity 10) at 4815, 
4771, 4738, 4709, 4686, then follow (intensity 4) 
4497, 4494, 4443, 4380, 4370, 4360, 4242, 4241, 
4228, 4210, 4209, and lastly (intensity 8) 4155, 4149. 

The five strong lines 4815 to 4686 are easily dis- 
tinguished in our spectrum; and 4155, 4149, may be 
picked out in the brighter part of the spectrum. There 
also appear metal lines beyond ; until, at the extreme 
violet end of the spectrum; we find two intense hnes, 
one midway between H^ and H*^, and the other a little 
beyond H^. 

Third Spectrum. Zirconium and Palladium 
Spark. — Small pieces of the metal in clips. Many in- 
dications of sharp metal lines on the upper (Zirconium) 
margin of spectrum about 4686, 4575, 4550, 4540, 
4530, 4380, 4370, 4228, and 4155, (the last two 
rather strong), and in other places. A line (two are 
seen in the original plate), appears also in this and the 
next spectrum at the extremity of the violet end, which 
probably corresponds with the intense one in the arc. 
Palladium margin weak, and lines not easily distin- 

Fourth Spectrum. Zirconium Spark. — Small 
flakes of the metal in the clips. Spectrum confined to 


centre, dark strong lines corresponding to 4228, and 
4155 in last spectrum well seen. Three lines (Iron ?) 
project from the upper margin of last spectrum in the 
region about G, which may be also identified in this 
spectrum. Note also line at extreme violet end. 


Scale and Solar Spectrum. — ^Both have been 
previously referred to and described. 

N.B. Potassium and Sodium were tried in arc and 
spark, but caught fire and would not last long enough 
to give an image. Caesium alum was tried (moistened 
in glass cup) with spark, but gave no result. Silicon 
in arc, the upper pole was quickly covered with a white 
crust of oxide which stopped the arc current. Tan- 
talum in arc gave only point hues. 


Some of the gases have been added by way of 
supplement to the arc and spark spectra. The set 
of the gas photographs is by no means complete ; and 
they are rather experimental than otherwise, as three 
different instruments have been used for their pro- 
duction, arid the one which gave the best results came 
last in the field. The spectroscopes employed have been 
already described in the Introduction ; and are there 
and in the following notes distinguished respectively as 
A, B and C. As the dispersion (to preserve light) was 


necevSsarily small, and as the gases give each a whole 
and complete spectrum due to itself, it has not been 
considered necessary to adapt a scale to the photographs. 
Some of the gases are compared, the one with the 
other ; and . others are compared with hydrogen, or 
show one or more of the hydrogen lines : and in this 
way a general idea is in most cases obtained of the 
position of the principal lines or bands in the spectrum 
without reference to scale. Of course individual aspect 
is still more marked in tlie case of the gas spectra than 
in the more complicated spark and arc spectra of the 
metals. The remarks appended to the gas spectra will 
mainly consist of notes as to the behaviour of the tubes 
and brief indications of any special features in the 


First Print. Line Spectrum of Nitrogen. 

Third Print. Band Spectrum of Nitrogen, 

Centre Print. Line and Band Spectra of 
Nitrogen compared. 

The first photograph (line only) was taken with 
spectroscope A. The centre and third with spectroscope 
C. Two nitrogen tubes were employed, the one with 
coarse capillary part for the line spectra, the other with 
fine capillary for the band spectra. 

The spectra were easily taken with twelve to fifteen 
minutes exposure, and the small coil was generally 
enough to work a single tube. To procure tlie line 


spectra, the condenser (with two plates only) was in- 
troduced into the circuit. The nitrogen line first spec- 
trum is remarkable for its brightness towards the red 
end, but with a falHng ofi* in light towards the violet. 
This feature seems characteristic of the line spectra in 
general. The line spectrum in the centre print is weak 
and poor in lines as compared with the first hne 
spectrum, partly perhaps for want of illumination in the 
tube, but mainly that being the side tube, (the band tube 
was in front of the slit) the image was weakened by 
reflection from the comparison prism used to obtain the 
second spectrum. 

A fine line is noticed on the extreme left of the 
band spectrum (centre print), which is attributed to 
F hydrogen, and serves to mark the position of the 
nitrogen bands. Twenty of these are counted in the 
lower band spectrum. 

NITROGEN (continued). 

First Print. Nitrogen Line and Band Spectra 

Second Print. Nitrogen Band. 

Third Print. Nitrogen Band and Hydrogen com- 

Fourth Print. Nitrogen Capillary part of Tube 
and Nitrogen Bulb part of Tube^ (near red pole, as dis- 
tinguished from violet pole on next plate), compared. 

All these were taken with the spectroscope B 
(quartz), and are on the smaller scale. In the nitrogen 


line and band compared spectrum, the band tube was 
in front of the slit and the line tube at the side. In the 
hydrogen and nitrogen compared spectra the hydrogen 
tube was in front, and the nitrogen at the side ; and 
unless the contrary is stated, it holds good throughout 
as to all the compared spectra, that the tube at the side 
is the upper spectrum and the tube in front of the slit 
is the lower spectrum in the resulting plate. 

As might be expected, the spectral images in the case 
of the quartz spectroscope lose somewhat towards the 
red end of the spectrum, but gain much in the direction 
of the violet. About as many of the nitrogen bands 
are counted as in the last plate, but they are not the 
same. They commence at the bright edge of the band 
spectrum in centre print of last plate, and extend con- 
siderably further into the violet. An examination of 
hydrogen and nitrogen compared spectra (third print) 
will illustrate this. The faint line to the extreme left is 
F hydrogen. The bright Une meeting the edge of the 
upper spectrum is near-G, the next is A, and then two 
other fainter lines of hydrogen. 


NITROGEN (continued). 

First Print. Nitrogen Band {Capillary) compared 
with Nitrogen Violet Pole. Spectroscope C. 

Second Print. Same, but reversed in position. 
Spectroscope B. 

Third Print. Violet Pole, — Spectroscope B. 

In the first (large) print the nitrogen capillary 



bands, probably from the tube not being well adjusted 
in front of the comparison prism, appear like lines. 
This is, however, not without advantage, as they thus 
indicate more clearly their position in regard to the 
violet pole hues and bands. F hydrogen may be seen 
as a faint line to the left of the violet pole spectrum in 
this print. The following wave lengths, as given by 
Dr. Vogel, may be interesting for comparison : — 



Capillary part of Tube. 

5066 bright. 



4862 very faint. 

4811 bright. 

4721 „ 

4666 faint. 

4644 bright. 

4570 very bright. 

4487 bright. 











Violet Pole. 

6147 feint. 
5002 bright. 


4808 very faint. 
4704 very intense. 

4646 very faint. 
4569 bright. 
4486 „ 
4417 very faint. 

4346 bright. 
4273 very bright. 

Our lines extend considerably more into the violet. 
The violet pole has attracted considerable attention in 
connection with the Spectrum of the Aurora, mainly o 


account of the late Prof. Angstrom's opinion, that ' the 
' feeble bands of the Aurora spectrum belong to the spec- 
' trum of the negative pole, possibly changed more or 
' less by additions from the banded or the line air 
' spectrum.' 


I have discussed tliis question at length in a paper, 
on the Aurora Spectrum, published in the ' Philoso- 
phical Magazine' for April 1875 ; and I only refer to 
it now to point out that the difficulty of actual line 
comparison which then existed might perhaps now 
be conquered. 

With one or other of the instruments we have used, 
there really seems no reason why a photographic 
image of the more refrangible rays of the Aurora Spec- 
trum should not be obtained without difficulty. I saw 
at Kyle Akin in Skye in September 1874, a fine double 
arc Aurora of great brilliancy which lighted up the 
whole landscape, and strongly impressed me with the 
idea that if proper apparatus had been at hand some- 
thing in that direction might have been accomplished. 
Auroras have unfortunately been quite quiescent lately. 
Should this state of things alter, the experiment would 
be well worth trying. As much as possible, say two 
thirds, of a long slit should be given to the Aurora, and 
the remaining one third kept in reserve for a com- 
parison spectrum. Dry plates might be used and a 
considerable amount of exposure given. The Camera 
should be directly pointed to the brightest part of the 
Aurora. After exposure and before disturbing the 
apparatus, the two thirds of the slit used for the Aurora 
should be covered, and the remaining third which was 
covered during exposure should be employed for the 
projection of a tube or solar spectrum on the same 

If a tube spectrum only were desired for comparison, 


a prism might be used on the slit in the usual way, but 
I prefer a direct image when practicable. 

To obtain absolute measurements of the lines a 
double slit (the upper half moveable by a micrometer 
screw) like one I have deposited at South Kensington, 
might be employed. Two photographic images being 
taken, one under the other, the lines are measured by the 
relative position of the same lines in the two images 
being compared with the ascertained value of the micro- 
meter movement. 


NITROGEN (continued). 

First Print. Band Spectrum of Nitrogen {Capillary) 
with Magnet. 

Second Print. Band Spectrum of Nitrogen 
{Capillary) without Magnet 

The Electro-magnetic experiments leading to these 
plates have been fully detailed in the Introduction : 
Spectroscope B (quartz) was used for them. The 
plate with magnet is brighter, especially towards the 

Centre Print. Ammonia {NH^ Tube, capillary 
part fine, tube lighted up easily. A nitrogen spectrum 
is alone prominent. 

Fourth Print. Line Spectrum of Nitrogen lube, and 
Spark in Air compared. — This print is from the original 
without enlargement, and does not show so much as 
the plate. The line tube spectrum was obtained by 
use of the Condenser in the usual manner. The spark 


passed between two platinum points introduced into 
the circuit. The stronger hues correspond in posi- 

Fifth Print, is introduced into the plate in con- 
nection with the second spectrum (Spark in Coal Gas) on 
Plate XXVII. 

The upper spectrum is that of spark in air as taken 
between Platinum points. The lower is spark in coal 
gas (after referred to) and the combined spectra are 
printed to illustrate the approximate position of the 
hues in the spectrum of spark in coal gas at ordinary- 
pressure as compared with spark in air. Spectroscope 
C was used. Image not very good, but better on plate 
than in the print. It would not bear enlargement with 
any advantage. 


First Print. Hydrogen Tube, — Small in capillary- 
part, lighted up well with small coil. A portion of 
the capillary bore, comprising the whole circumference 
of the tube is decomposed, and has the appearance of 
being obscured by a yellow white coating. The 
bright red tint of the discharge was lost here, and 
the lines of the spectrum were partly extinguished 
in a white misty haze. This effect is seen in the 


The spectrum, as to principal hues, will be seen to 
consist of — 


No. 1. F. 4861. 

2. Near-G, 4340 (G 4307). 

3. A 4101. 

4. A sharp bright line, not quite as distant 

from h as h is from G. 

5. A line faintly seen in the print beyond 

No. 4, not quite as distant from No. 4, as 
No. 4 js from h. 

No. 5, in the original plate, is fairly strong, and 
close to, and on each side of it, are also seen two single 
fine lines, the one on the violet side being rather the 
more distant (see also Centre Print, Plate XXVIII.). 

Lines of some breadth and intensity are to be 
remarked between the more prominent lines before 
described. Two short ones between No. 1 and No. 2 
(five are counted on the plate), three or more between 
No. 2 and No. 3, and three between No. 4 and No. 5. 
The spectrum is also filled with a number of very 
fine and sharp lines, traces of which are indicated in 
the print. Whether these intermediate lines are due 
to hydrogen or to tube impurity is not clear ; but as 
some of the coarser ones are traced in the second 
spectrum on next plate, (Spark in Coal Gas), it is 
probable that these at least are due to the gas. 

Second Print. Spark in Coal Gas. — ^This spectrum 
and the way it was obtained have been already 
described in connection with the Carbon Spectra. 
Another but less bright print is found on Plate VL 

This spectrum is on the same scale as the arc 
and spark spectra, and therefore larger than our Gas 


spectra in general. Tlie original, before enlargement 
is found on Plate XXXIII. The print is liere intro- 
duced to illustrate the expansion of a hydrogen line. 
Note traces of a narrow dark space dividing the centre 
of the expanded line. The sharp hues are attributed 
to Carbon. 

Third Print. Hydrogen Tube^ taken with spectro- 
scope B, wide sht. Lines 1, 2, 3, 4, and 5, in last 
spectrum are brightly seen, (No. 5 very bright), a sixth 
is easily traced some distance beyond, and a seventh 
faintly indicated where the continuous spectrum ends. 

HYDROGEN (continued). 

First Print, Compared spectrum. Spark in Air 
between Platinum Points^ and Hydi^ogen Tube, — Spectro- 
scope C. Large coil and condenser used for spark. 
Small coil for the tube. Exposure for tube 15 minutes, 
for spark 5. 

The spark spectrum is seen to extend far into the 
violet ; considerably beyond the spark in air, as taken 
in combination with the metals. The four principal 
hydrogen lines, commencing with F, are well seen, 
some intermediate ones faintly. 

Near-G is the only hydrogen line that can be 
absolutely traced into and through the air spectrum. 

Second Print. Spark in Coal Gas at ordinary 
pressure, — The manner in which this spectrum was 
obtained has been described under tlie head of Carbon 


among the Arc and Spark Spectra, and the peculiar 
difference between this and the print, on Plate XXVI. 
(also spark in Coal Gas) has been noticed. 

This spectrum should be compared with the first 
print in this plate, (Spark and Hydrogen) arid 
with hydrogen on the last plate. TKe image is en- 
larged very slightly more than the other two spectra, 
but not enough to prevent easy comparison. Taking 
the principal lines of Hydrogen in their order, — 

F is seen as a bold very bright expanded line. 

Near-G is seen to the left of a well defined line 
not found in the ordinary hydrogen spectrum, as a 
still more expanded bright band or stripe with conical 
ends. A bright sharp line between F and near-G, 
surrounded by a nebulous halo coincides with one of 
two short lines in the hydrogen tube. 

Beyond near-G, we have a blaze of continuous 
spectrum, crossed by four prominent lines. 

The first of these lines has been already noticed, 
and does not appear in the hydrogen spectrum. 

The second falls very close upon the place of h 
in the hydrogen tube. 

The third does not appear in the hydrogen tube. 

The fourth, and last, and the most expanded, falls 
close upon the place of No. 5 in the hydrogen spectrum. 

Intermediate of Nos. 1 and 2, and of Nos. 2 and 3, 
are faintly but distinctly traced some of the less strong 
lines of the hydrogen tube. The general position of 
this spectrum as compared with air is indicated by the 
small print on Plate XXV. before described. 



First Print. Band Spectrum of Oxygen^ tube 
No. 1^ spectroscope C. 

Second Print. Band Spectrum of Oxygen^ tube 
No. 2, same spectroscope. 

These two tubes were worked by the larger coil, 
with batteries purposely weak; exposure fifteen 
minutes. In the case of No. 1 tube the colour of the 
capillary stream was a pale pink. There was consi- 
derable stratification in tlie bulbs of both tubes. 

The spectrum of No, 1 is a short bright one, com- 
posed of a mixture of oxygen and hydrogen lines, the 
latter probably due to moisture in the tube. F hydro- 
gen is seen as a single line to the extreme left; 
near-G is seen very bright at the edge of the illuminated 
part of the spectrum, h is seen in the centre of the 
spectrum, apparently doubled by a strong oxygen line. 
The other less distinct lines or bands are those of 
oxygen. In the plate some finer lines are seen inter- 
mediate of the coarser ones. Professor Draper is said 
to have recently found some of the oxygen Unes as 
bright ones in the solar spectrum. 

The capillary stream of tube No. 2 was somewhat 
redder in tint. The spectrum was taken and enlarged 
as one of oxygen, to accompany that of No. 1 ; but a 
comparison with the upper print on Plate XXVI. will 
show that while the continuous spectrum and some 



indistinct lines or bands are probably due to oxygen, 
the principal bright lines are those of hydrogen. It 
will be noticed, too, that the triple line mentioned as . 
No. 5 and feintly seen in the hydrogen spectrum, shows 
in the spectrum now examining (to the extreme right) 
as a strong double line, with shading off towards the 

Third Spectrum. Line Spectrum of Oxygen. — 
This was obtained in the usual way, by introduction of 
the Condenser (with two plates) into the circuit. The 
spectroscope used was A. 

Four line spectra are printed which have been 
taken with this instrument : Nitrogen, Plate XXTI. ; 
the present (Oxygen) ; Carbonic Acid, Plate XXX. ; 
and Coal Gas, Plate XXXIII. Each of the three last 
spectra, though differing in other respects, has a marked 
character in common, viz, a bright line to the left, 
as jumed to be F hydrogen, and a bright broad band of 
light more towards the centre with a sharp line close 
adjoining on the violet side. The other lines by their 
variation show that the spectra, as a whole, are not 
by any means identical; but these particulars seem 
constant. It might be expected that the bright line 
adjoining the band would be ' near~G ' hydrogen, but 
this is not the case. An examination of the original 
plates shows that the enlargements are strictly correct, 
and that the broad band itself exactly occupies the 
place of ' near-G ' in the hydrogen spectrum. It would 
seem that the images of spectroscope A give the line 
spectrum towards the red end, while those of spectro 


scope B (quartz) give the line spectrum towards tlie 
violet (see Plate XXTX. line oxygen). 

OXYGEN (continued). 

All the photographs on this plate were taken with 
spectroscope B (quartz). 

First Print. Band Spectrum of Oxygen^ tube No. 1. 
— This spectrum extends, in an even series of bands, 
considerably into the violet. In the spectrum of 
oxygen on last plate, we count only six principal coarse 
lines or bands. In this print we count no less than 
fifteen. Probably from some difference in lighting up 
of the tube, one hydrogen line only shows in this 
spectrum, and the bright oxygen line doubling the 
hydrogen line in the spectrum on last plate though 
present is not nearly so conspicuous. 

Print No. 2. Water Gas.—T\ibG marked HgO, 
worked as above, colour of capillary red, but not so 
red as hydrogen. The principal lines of the latter are 
well distinguished. The oxygen spectrum is not so 
bright, especially towards the violet as in the last print. 

Third Print. Band Spectra of Oxygen and Ni- 
trogen compared. — Nitrogen tube and spectrum much 
the brightest. Oxygen spectrum towards red a com- 
paratively even set of bands. Nitrogen, in sets of 

Fourth Print^ Line and Band Spectra of Oxygen 

F 2 


compared. — Line tube the brightest. Line spectrum 
very bright towards the red, but obscured towards the 


First Spectrum. Band Spectrum of Carbonic Add. 
— Spectroscope C. Tube marked C A of rather large 
bore, worked by large coil, much stratification extending 
even through the capillary, stream of capillary light, 
bright and of silvery grey green tint. Spectrum much 
filled up by obscure sets of bands or lines, except in the 
positions occupied by a bright line in the centre and a 
dark space more towards the violet. F hydrogen shows 
to tlie extreme left. The other hydrogen lines are not 
seen. Note sharp bright line separated from main 
body of the spectrum towards the red. 

Second Print. Spectroscope C. — This was a tube 
marked SO3. The light was pearly white. The 
spectrum turned out to be carbonic acid, probably 
from some impurity in the tube. See also second and 
third prints on Plate XXXV. The tube was worked 
by the large coil and two weak bichromates. 

Third Print. Line Spectrum of Carbonic Acid. 
— Spectroscope A. Condenser in circuit. Tube filled 
with stream of white light. Compare line spectra of 
oxygen and of coal gas taken with same instrument. 



CARBONIC ACID (continued). 

First Print. Spectral image, taken with spectro- 
scope A, of capillary part of carbonic acid tube (C A) 
wide slit. Stratification well seen. Print from original 
negative not enlarged. 

The three remaining spectra on this plate were 
taken with spectroscope B. 

Second Print. Carbonic Acid Tube^ Band Spectrum, 
— This spectrum \xa taken with the quartz instrument, 
though the same, differs somewhat in actual appearance 
from our print on last page. The two left-hand single 
lines are absent. The left-hand edge of the centre 
part of the spectrum is comparatively brighter. The 
bright band and dark interval before referred to are 
still more strongly defined. 

Beyond the bright band and next to the dark inter- 
val which nearly ends the spectrum on the last plate, 
we get in our present spectrum a set of six lines or 
bands, the first only of which is faintly indicated in the 
spectrum taken with instrument C. 

Thjrd Print. Line Spectrum of Carbonic Acid 
compared with Line Spectrum of Oxygen. 

Fourth Print. Band Spectrum of Carbonic Acid 
compared with Band Spectrum of Oxygen. 

Some years ago Mr. Henry K. Procter and myself 
were much struck with the closeness in position of the 
three prominent briglit lines or bands in the yellow, 


green, green and blue, in hydrocarbon tubes as compared 
with like lines in an oxygen tube. The three lines 
were so nearly identical in position in the compared 
tubes that a fine pointer and high power eyepiece 
failed to distinguish apart their sharper margins. But 
for a certain want of accord in tint and intensity of the 
two spectra, we began to suspect the identity of the 
oxygen spectrum, and Mr. Procter even conjectured 
that oxygen might have only a continuous spectrum, 
and that the bright lines might arise from carbon 
impurity in the tubes. 

Our compared photographic spectra lie much more 
towards the violet end of the spectrum (beginning with 
the more refrangible of the three lines or bands above 
referred to), but it is pretty clear from an examination 
of them that, in this part of the spectrum at least, the 
spectra differ considerably. The line spectra approach 
the nearest in position, but there is a marked and 
distinct character to each of these. The band spectra 
are widely different. The smooth and even character 
of the band spectrum of oxygen contrasts strongly 
with the sharper and more defined lines and bands of 
the carbon spectrum. Some few lines only towards 
the violet of carbonic acid appear to correspond with 
bands in the oxygen spectrum. The one extremely 
bright line or band in carbonic acid is conspicuous 
for its absence as such in oxygen. 



First Print. Band Spectrum of Coal Gas. — Spec- 
troscope C. Stream in tube whiter and brighter 
than carbonic acid, much stratification, exposure 15 
minutes. Spectrum as reading from the red composed 
of foiu: faint single hues followed by an evenly lighted 
broad continuous portion, crossed by many well-defined 
briglit lines or narrow bands. 

This continuous portion terminates with a most bril- 
liant band or set of lines shading ofi* towards the violet, 
which is immediately succeeded by a fairly strong and 
then a faint Une as the last indication of the spectrum. 

Compared with the Hydrogen spectrum, F is 
seen faintly to the extreme left, foUow^ed by the two 
short Unes seen in the Hydrogen spectrum between F 
and near-G. Next comes an outstanding sharp line, 
also seen in the Carbonic Acid spectrum. 

Near-G Hydrogen is next seen as a well-defined 
line on the edge of tlie conthiuous portion. The 
very bright line exactly in the centre of the print does not 
fall in the place of h but of a line a little beyond A, also 
seen in the Hydrogen spectrum. The spectrum forms 
a fine photograph, and nearly all that is seen in the 
plate is got out in the print. 

Second Print. Cyanogen, — Tube lent to me by 
Mr. W. G. Lettsom, lighted up easily with a white 
glow, fines and bands sharper and more separated by 


dark intervals than in the Coal Gas spectrum. As- 
suming the first (single) line on the left to be near-O 
Hydrogen, a few lines in the spectra of coal gas and 
cyanogen fairly correspond, and the general character 
of the two spectra is somewhat alike. They, however, 
differ in detail. 

Third Print. Coal Gas Tube. — Spectroscope B. 
The general aspect of the spectrum is that of the first 
print, except that the lines are not so well defined, but 
blend into bands. 

The especially bright band towards the violet is 
easily recognised, and beyond it extend three bright 
bands not seen in the large spectrum. 

COAL (?ul/Sf (continued). 

First Print. Line Spectrum of Coal Gas. — Con- 
denser in circuit, exposure 20 minutes. Note former 
remarks on line spectra of oxygen and carbonic 

Second Print. Line and Band Spectra of Coal Gas 
compared. — ^The line spectrum commences with the 
band and bright hue so conspicuous in the first print, 
and then succeed two other bright lines or bands, with 
fine lines between. The last band towards the violet 
in the line spectrum corresponds with the very bright 
band in the band spectrum. 

Third Print. Coal Gas Band Spectrum compared 


with Hydrogen Lines, — Spectroscope A. Print from the 
original negative, not enlarged; near-G is seen on the 
edge of the first bright band or set of lines in coal 

Fourth Print. Spark in Coal Gas at ordinary 
pressure. — Same spectroscope as used for Arc and Spark 
Spectra. Print from original negative, v^hich was after- 
wards enlarged to form prints on Plates VI. and 


First Print. Olejiant Gas. — Tube fairly bright. 
Spectroscope A. A broad bright band, (probably a set 
of lines or bands), and a nebulous bright line beyond, 
towards the violet, are very marked in this spectrum. 
As these are only feebly indicated in the other two 
spectra of this gas, they may probably have depended 
upon the lighting up of the tube. 

Second Print. Olejiant Gas. — Spectroscope C. 
Spectrum Avith w^ell-defined lines. The faint one 
towards the extreme left seems to be one of the lines in 
Hydrogen intermediate of F and near-G. As in the 
case of coal gas, near-G is on the margin of the con- 
tinuous part of the spectrum, while the fifth bright line 
in the spectrum falls upon the place of the line in 
Hydrogen just beyond h. 

The bright broad band in the first print is indicated 
by a few faint lines. 


Third Print. Olejiant Gas, — Spectroscope B. 
The set of two double and two single bright lines in the 
last spectrum is easily recognised on a smaller scale. 
Three other bright bands are seen towards the violet. 

Fourth Print. Turpentine Vapour, — Tube not 
bright, large coil used. Exposure fifteen minutes. 
As might be expected, the print bears a likeness to the 
Olefiant spectrum. 

Fifth Spectrum. Ether Vapour, — Spectroscope C^ 
tube difficult to light up. What is seen of spectrum 
resembles Olefiant and Turpentine spectra. 



First Print. Sulphur. — A short German tube, 
with small bulbs and a bent capillary part. The bulbs 
contained a small quantity 'of solid sulphur. The tube 
was suspended, and the lower bulb heated by a spirit- 
lamp. When the sulphur was partly melted, one half 
of the capillary was white in colour and the other half 
red. As the heat was gradually applied the spectrum 
of sulphur of first order was seen to spread up the tube 
as a set of bright bands, which by management of the 
lamp could be kept at a definite height. The spectrum 
independent of the sulphur vapour was found to be 
hydrogen, with the principal lines very bright. Photo- 
graphs were first tried with A and B spectroscopes, but 
were not satisfactory. Several plates were subsequently 


taken with spectroscope C. We tried to take tlie spec- 
trum lower lialf sulphur and upper half hydrogen, but 
failed, probably for want of proper adjustment of the 
lamp. In each case we found only the sulphur spec- 
trum on the plate. The plates were all much alike, and 
only differed in distinctness of the bands. 

Second Print. Another print of SO3 Tube Spec- 
trum. — Spectroscope C, see Plate XXX., where by con- 
parison the spectrum is seen to be a carbonic acid one, 
arising we presume from impurity in the tube. 

Third Print. SO^^ Tube. — Spectroscope B, same 
result as above. Compare with carbonic acid spectra, 
Plate XXXI. The slit must have been a little wider, 
or the tube less bright in this instance, as the spectrum 
is more continuous and the lines not so sharp. 


First Print. Silicic Fluoride Spectrum. — Tube 
easily worked, capillary a beautiful violet, bulbs golden 
brown. Under mfiuence of large electro-magnet, stream 
of light became less violet and more red in tint, con- 
tracted itself, and ran through the bulbs from pole to 
pole. At the same time a slight noise, between a 
whistling and a metallic ring of high pitch, was heard. 

The stream was curved in the bulbs towards one 
side or the other as the current was reversed. Good 
photograph, lines some twenty- four in number, sharp, 
and well separated. A fine shaded group commences 
the spectrum towards the red end. This group in 


the spectroscope is of a brilliant violet tint, and at once 
identifies the spectrum. 

Second Print. Silicic Fluoride Spectrum, — Spec- 
troscope B. The spectrum does not seem more ex- 
tended into the violet in this instance, but a band or 
set of lines towards the centre is brightened up. A 
second photograph was taken with the tube under the 
influence of the electro-magnet, same time of exposure. 
The image was identical, but very decidedly fainter. 

Third Print. Tin Chloride. — Spectroscope B. This 
tube was very difficult to photograph. The small coil 
only did not sufficiently light the tube, the large coil 
was too much for it. The discharge was in the form 
of a slender bright green thread running through the 
tube. Forashorttime all went well, after that the stream 
intermitted and almost broke up, and flashes of light 
only took its place. At the same time the metal lines 
grew fainter in the spectrum, and the bulbs of the tube 
were filled with a yellowish flare. These, on subsequent 
examination, were found covered with a whitish crust. 
Only one fair plate was obtained, of which a print is 
given. Some fine metallic looking lines seen in the 
spectrum do not come out in the photograph. 

Fourth Print. Iodine Tube. — ^This was lighted by 
the small coil only. The photograph shows two sets of 
bands, each gradually degrading towards the violet, with 
a dark interval between them. 

Many fine lines seen in the tube spectrum do not 
appear in the photograph. 

Fifth Print. Spark in Iodine Vapour. — A bulb 


similar to that employed for spark in coal gas was used. 
The ends were lightly plugged with cork and the iodine 
vapourised by a spirit-lamp. 

When the vapour filled the bulb, the spark spectrum 
as seen through it with a small direct vision spectro- 
scope showed marked absorption bands. 

Traces of these (better on the plate than in the 
print) may be found on the photograph. 

A Chlorine Tube^ it has been mentioned, baffled us. 
We tried it with the small coil, and exposure gave no 
image apparently for want of brightness. We then 
tried it with the larger coil. At first the tube shone 
with a yellowish green stream running from pole to 
pole, the bulbs being filled with a somewhat dull purple 
glow. Almost suddenly one pole and then the other 
changed to a brighter and whiter purple. One pole 
then changed to a rich salmon colour, the opposite 
pole remaining white surrounded by a purple glow. 
Current reversed, and both bulbs then became salmon 
colour, with considerable stratification. Ultimately the 
capillary became a pinkish white, one pole a red buff 
and the other a bright lilac. The yellow green line 
was then altogether lost. 

On reversing current, the poles changed. The 
spectrum when the plate was examined was found to 
be nitrogen. 


^ I. 




notp: to oxygen 8PECTRUM. 

Since the foregoing has been penned, Professor Draper's in- 
teresting paper and photograph have been made public. 
The solar spectrum from about 4350 to 3900 is photo- 
graphically compared with the lines of oxygen, as seen in 
spark in air, and coincidences are sliown, principally at the 
double lines 4319 4317, 4190 4184, and tlie triple line 
4076 4072 4069. The air spark spectrum in Professor 
Draper's photograph, making allowance that it is on a scale 
of three times the size, and that it has less of continuous 
spectrum filling up between the lines, very closely resembles 
our air spectrum fine slit Plate I. Most of the lines 
in each are easily compared and identified. The three 
principal nitrogen lines are recognised, the one near 4000 
by its strength and brightness, and the other two by 
their fuzzy expanded character : the oxygen lines by their 
comparative sharpness. In our solar spectrum, we find 
faint traces of the bright lines which are alluded to by 
Professor Draper, and their character suggested. It is 
curious that these bright lines in the solar spectrum should 
have been so long overlooked, or not more closely examined ; 
for in the spectrum taken from an illuminated cloud 
with a large direct vision spectroscope their existence is 
readily detected. Doubtless they have been generally re- 
garded as spaces or effect of contrast between the dark lines, 
and it is indeed only after a certain amount of study whether 
of the spectrum or of a photograph, that they appear to 
stand forward from among the dark lines in an independent 
character. Judging from his paper, Professor Draper seems 
to have found with his incompara))ly larger and more perfect 



apparatus, the same sort of diEBeulty in the tube work that 
we experienced in ours on a smaller scale. Professor Draper 
makes the remark, ' I do not think that in comparisons of 
the spectra of the elements and smi, enough stress has been 
laid on the general appearo/nce of Imea apart from tkevr mere 
position ; in photographic representatioDs this point is very 

Our set of Plates amply illustrates the justice of this 
remark of the Professor's, 


Air wide Slit . 

Air fine Slit . 

Arsenic Spark 

Aluminium Spark . 

Aluminium Arc 

Antimony Spark 

Antimony Arc 

Bismuth Spark 

Bismuth and Nickel Spark 

Bismuth and Tellurium Spark 

Bismuth Arc . 

Barium Spark 

Beryllium (Iron) Arc 

Boron Arc 

Calcium (Zinc) Spark 

Cadmium Spark 

Cadmium Arc . . 

Carbon Points 

Carhon Points ruled out 

Coal Gas Spark in . 

Chromiaim Arc 

Cohalt Arc . 

Copper Spark . 

Copper Arc . 

Copper and Silver Arc 

Copper, Gold, and Silver (Alloy) Arc 

Copper and Iron Spark 

Didymium Arc 

Erhiaim Arc . 

Gold Arc 

Indium Arc . 

Indium Spark 











/. XVII. 19, 




II. X. 

19, .34 

















































VIII. . 




82 INDEX. 

PLaTR pagb 

Iridium Arc ........ Vin. 30 

Iron and Copper Spark VIII. 31 

Iron and Copper Spark IX. 31 

Iron Arc IX. 31 

Iron Arc " . . IX. 31 

Iron and Selenium Spark IX. 32 

Iron Meteoric Arc ....*.. X. 33 

Iron Meteorite Arc X. 33 

Lead Arc X. 34 

Lead and Antimony Spark X. 34 

Lead and Magnesium Spark XI. 35 

Magnesium and Lead Spark XI. 35 

Magnesium Spark XI. 35 

Magnesium Arc * XI. 35 

Manganese Arc XII. 36 

Manganese Arc XII. 36 

Mercury Spark XII. 37 

Molybdenum Arc XII. 37 

Nickel Arc . Xm. 38 

Nickel Spark in. 20 

Niobium Arc . . XIII. 38 

Palladium Arc XHI. 39 

Palladium Spark XVH. XX. 47, 48, 53 

Platinum Arc . . * XIII. 39 

Rhodium Arc . XIV. 40 

Rutbenium Arc XTV. 40 

Scale L XXI. 17 

Selenimn and Tellurium Spark .... XTV. 40 

Selenium and Iron Spark IX. 32 

Selenium and Aluminium Spark .... XTV. 40 

Silver Spark XV. 42 

SHverArc ....'.... XV. 42 

Silver and Copper (Alloy) Arc .... XV. 43 

Solar Spectrum XV. XXI. 43 

Strontium Spark XVI. 44 

Tellurium Spark . . . . .HI. XIV. XVI. 20, 40, 45 

Thallium and Indium Spark XVI. 45 

Thallium Arc. . . - XVI. 47 

Titanium Spark . XVH. 47 

Titanium, Aluminium, and Palladium Spark . . XVII. 47 

Titanium Arc XVII. 47 

Tin Arc XVIL 49 

Tin and Zinc Spark XVIII. 49 

Tin and Zinc Spark XVIII. 49 



Uranium Arc . 

Vanadium Arc 

Wolfram Arc . 

Yttrium Arc . 

Zinc Alloy (Brass) Arc . 

Zinc Alloy (Brass) Spark 

Zinc and Tin Spark 

Zinc Arc 

Zirconium Arc 

Zirconium and Palladium Spark 

Zirconium Spark 


























Ammonia .... 
Carbonic Acid Band 
Carbonic Acid Band [SO3] 

Band Quartz . 
Stratification . 
Band and O, Band 
Line and O. Line 
Coal Gas Band 

Band Quartz . 

Line and Band 
Band and H 
Spark in . 
Spark in, and Spark 
Ether Vapour 
Hydrogen Tube 

in Coal Gas . 
Quartz . 
and Spark in Air 
Lines in Coal Gas 
Iodine Vapour 
„ Spark in 
Nitrogen Line 




in Air 


XXV. 60 

XXX. 68 

XXX. 68 

XXX. 68 

. XXXI. 69 

. XXXI. 69 

. XXXI. 69 

. XXXI. 69 

. XXXII. 71 

. XXXII. 72 

. XXXIII. 72 

. XXXIII. 72 

. XXXIIL 72 

XXV. 61 

. XXXII. 71 

. XXXIV. 74 

. XXVI. 61 

. XXVI. 62 

. XXVI. 63 

. XXVII. 63 

. XXVII. 63 

. XXXVI. 76 

. XXXVI. 76 

. XXII. 55 


84 INDEX. 


Nitrogen Line and Band XXII. 56 

„ Band XXII. 65 

„ Band Quartz XXIII. 56 

„ Line and Baud , . . . . XXIII. 56 

„ Capillary and Bulb XXIII. 56 

„ Band and H XXIIL 56 

„ Band (Capillaiy) and Violet Pole . . XXIV. 57 

„ Violet Pole Quartz XXIV. 67 

„ Violet Pole and Capillary . . . XXIV. 57 

„ without Magnet XXV. 60 

„ with Magnet . . . . . . XXV. 60 

„ Line and Spark in Air .... XXV. 60 

„ Spark in Air and Spark in Coal G^as . . XXV. 61 

defiant XXXIV. 73 

„ XXXIV. 73 

„ Quartz XXXIV. 74 

Oxygen Band, Tuhe No. 1 XXVIH. 65 

„ „ Tube No. 2 . . . . , XXVin. 65 

„ Line XXVin. 66 

„ Band Quartz XXIX. 67 

„ (Water Gas) . . . . . . XXIX. 67 

„ Line and Band XXIX. 67 

„ Band and Nitrogen Band .... XXIX. 67 

SiHcic Fluoride XXXVI. 75 

„ Quartz XXXVI. 76 

Sulphur XXXV. 74 

Sulphuric Acid [SOg] XXX. XXXV. 68,75 

„ Quartz . XXXV. 75 

Tin Chloride XXXVI. 76 

Turpentine Vapour XXXIV. 74 

LosDoy : rnixTBD ay 


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CALCIUM, (zinc) spark 



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